tl;dr: Please put your code into a
`YOUR CODE`
section.. Hello everyone! Algorithm to find longest common prefix of a set of strings Solving particularly for two string, the problem is not that difficult what it is for a set of strings. In recursion, we start comparing the strings … Programming Tutorials. SequenceMatcher in Python for Longest Common Substring. To solve this, we will take the first string as curr, now take each string from the array and read them character by character, and check the characters between curr, and the taken string one by one. For example, given two strings: 'academy' and 'abracadabra', the common and the longest is 'acad'. Find First Non-repeating character in a string Find the Longest Common Prefix using Python. Write a function to find the longest common prefix string amongst an array of strings. There are several algorithms to solve this problem such as Generalized suffix tree. Problem Note. The common prefix is ca. Longest Common Prefix in Python; Find minimum shift for longest common prefix in C++; How to find the longest common substring from more than two strings in Python? All of these implementations also use O(nm) storage. There are two approaches to solve it: Case 1: Match every single word to check for the prefixes. For example, given two strings: 'academy' and 'abracadabra', the common and the longest is 'acad'. So, if the input is like ["antivirus", "anticlockwise", "antigravity"], then the … Python (Longest common prefix) Write a method that returns the longest common prefix of two strings.For example, the longest common prefix of distance and disinfection is dis.The header of the method is: def prefix(s1, s2) If the two strings have no common prefix, the method returns an empty string. Longest Common Prefix - LeetCode. Solution Class longestCommonPrefix Function Solution Class lcp Function longestCommonPrefix Function. For Example, longest common prefix of "abcdefgh" and "abcefgh" is "abc". Longest Common Prefix: Given the array of strings A, you need to find the longest string S which is the prefix of ALL the strings in the array. Here we will assume that all strings are lower case strings. Another example: ''ababc', 'abcdaba'. So the algorithm is pretty simple, scan from the first character, if it is same for all the strings… DO READ the post and comments firstly. Add to List. For this one, we have two substrings with length of 3: 'abc' and 'aba'. One just has to check on the prefixes of each string. So we can make use of the above associative property to find the LCP of the given strings. For a string P with characters P 1, P 2,…, P q, let us denote by P[i, j] the substring P i, P i+1,…, P j. Write a program that takes 2 strings as input, and returns the longest common prefix. The characters obtained along such a path is our required longest common prefix. Problem Description. If you had some troubles in debugging your solution, please try to ask for help on StackOverflow, instead of here. All of these implementations also use O(nm) storage. I have been trying to solve a modification of the Longest Common Prefix problem. If you want to ask a question about the solution. The idea is to apply binary search method to find the string with maximum value L, which is common prefix of all of the strings. In this tutorial, I am going to discuss the algorithm and their java implementation to find the longest common prefix amongst an array of strings. string arr [] = {"geeksforgeeks", "geeks", "geek", "geezer"}; int n = sizeof (arr) / sizeof (arr [0]); string ans = commonPrefix (arr, n); if (ans.length ()) cout << "The longest common prefix is ". Constraints. Here we will assume that all strings are lower case strings. Find the Longest Common Prefix String Java Code. If you had some troubles in debugging your solution, please try to ask for help on StackOverflow, instead of here. Program for longest common directory path in Python, Find the longest common prefix between two strings after performing swaps on second string in C++, C++ Program for Longest Common Subsequence, Java Program for Longest Common Subsequence, Program to find length of longest common subsequence of three strings in Python. Approach for Longest Common Prefix using Trie. Longest Common Prefix Problem Statement Write a function to find the longest common prefix string amongst an array of strings. This problem can be found on Leetcode.. Write a function to find the longest common prefix string amongst an array of strings. LCP (string1, string2, string3) = LCP (LCP (string1, string2), string3) Like here LCP (“geeksforgeeks”, “geeks”, “geek”) = LCP (LCP (“geeksforgeeks”, “geeks”), “geek”) = LCP (“geeks”, “geek”) = “geek”. If there is no common prefix, return an empty string "" Please like the video, this really motivates us to make more such videos and helps us to grow. Hello fellow devs ! Input: technique, technician, technology, technical Output: The longest common prefix is techn Input: techie delight, tech, techie, technology, technical Output: The longest common prefix is tech Simple solution is to consider each string one at a time, and calculate its longest common prefix with the longest common prefix of strings processed so far. [Java]public… Abstract. Length of the longest common subsequence in Python. Write a program that takes 2 strings as input, and returns the longest common prefix. Algorithm for Longest Common Prefix using Trie Given the array of strings S, write a program to find the longest common prefix string which is the prefix of all the strings in the array.. Example 1: Input: ["flower","flow","flight"] Output: "fl" ~ "for all members x of set R, it holds true that string S is a prefix of x" (help here: does not express that S is the longest common prefix of x) An example use case for this: given a set of phone numbers, identify a common dialing code. Subscribe to receive an email every week for FREE, Subscribe to receive an email every week for FREE and boost your Software Engineering midset, All content copyright to Andrew O - Â© 2020. We start by inserting all keys into trie. We’ll use the first string in the array as our reference for checking the longest common prefix. common_suffix can be written as return common_prefix(string[::-1])[::-1] because the operations are just the simmetric of one another, and this way will prevent duplication.. Also I think you should not handle max or min inside the common_prefix function because it feels like the function has double responsabilty: finding prefixes + length interval check. Output Format Return longest common prefix of all strings in … To solve this problem, we need to find the two loop conditions. define base cases (n = 0,1). Then we traverse the trie until we find a leaf node or node with more than one child. Then we traverse the trie until we find a leaf node It is defined below. tl;dr: Please put your code into a
`YOUR CODE`
section.. Hello everyone! All given inputs are in lowercase lettersÂ a-z. Easy. Easy. Then, traverse an array from 1 to n-1 and find the common prefix between all the words. S n ] strings. Longest Common Prefix Write a function to find the longest common prefix string amongst an array of strings. The idea here is to assign a string present at the 0th index of an array in a variable and assume it’s a longest common prefix. Note: when using indexOf, an empty string will be considered at the 0th index, so if there is no common prefix, then the empty string will be returned. If there is no common prefix, return an empty string "". If there is no common prefix, return an empty string "". Define a string and calculate its length. Longest common prefix simply means the longest prefix (prefix is a substring also, but not vice-versa) all the member strings consist of. 0 ≤ strs.length ≤ 200; 0 ≤ strs[i].length ≤ 200; strs[i] consists of … Case 2: Sort the set of strings to find the longest common prefix. Difficulty: HardAsked in: Amazon, Google Understanding the problem. The longest common subsequence (or LCS) of groups A and B is the longest group of elements from A and B that are common between the two groups and in the same order in each group.For example, the sequences "1234" and "1224533324" have an LCS of "1234": 1234 1224533324. Case 2: Sort the set of strings to find the longest common prefix. The termination conditions are: (1) one string ends, then the longest prefix is the string itself. Analysis. If there is no common prefix, return an empty string "". If there is no common prefix, return an empty string "". Find the longest common prefix between two strings after performing swaps on second string in C++; Program to find length of longest common subsequence in C++ The longest common subsequence (or LCS) of groups A and B is the longest group of elements from A and B that are common between the two groups and in the same order in each group.For example, the sequences "1234" and "1224533324" have an LCS of "1234": 1234 1224533324. I'm comparing my algorithms, slice_prefix and bit_prefix, with existing ones to find the common prefix length of 2 strings as fast as possible. To find the length of the longest common subsequence, two popular techniques are – 1.Recursion. July 19, 2020 July 19, 2020; The challenge. Approach for Longest Common Prefix using Trie. If the string we pick (0) is not the shortest, the if condition will break the loops. Algorithm for Longest Common Prefix using Trie If there is no common prefix, return an empty string "". Example 1: Input: ["flower","flow","flight"] Output: "fl" Input Format The only argument given is an array of strings A. Longest Common Prefix http://www.goodtecher.com/leetcode-14-longest-common-prefix/ LeetCode Tutorial by GoodTecher. Analysis: Note that we have an array of strings, where we only need the common prefix, for all these strings. Algorithm to find longest common prefix of a set of strings Solving particularly for two string, the problem is not that difficult what it is for a set of strings. Another program I'm working with spends most of its time on one line len(os.path.commonprefix((item1, item2))).I've searched for other algorithms in Python and created my own to reduce this bottleneck. Input: technique, technician, technology, technical Output: The longest common prefix is techn Input: techie delight, tech, techie, technology, technical Output: The longest common prefix is tech Simple solution is to consider each string one at a time, and calculate its longest common prefix with the longest common prefix of strings processed so far. In the above string, the substring bdf is the longest sequence which has been repeated twice.. Algorithm. common_suffix can be written as return common_prefix(string[::-1])[::-1] because the operations are just the simmetric of one another, and this way will prevent duplication.. Also I think you should not handle max or min inside the common_prefix function because it feels like the function has double responsabilty: finding prefixes + length interval check. We can see that the longest common prefix holds the associative property, i.e-. Write a function to find the longest common prefix string amongst an array of strings. The longest common substrings of a set of strings can be found by building a generalized suffix tree for the strings, and then finding the deepest internal nodes which have leaf nodes from all the strings … If there is no common prefix, return an empty string "". Method implemented is not important. There are several algorithms to solve this problem such as Generalized suffix tree. However our current project was written in python 2.6, so "Counter" is … In this test case, the longest common prefix of characters among the three strings is "fl" In : # assert longest_common_prefix(["flower", "flow", "flight"]) == "fl" In this test case, there are no common prefix characters among the three strings so the function should return an empty string. Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix, return an empty string "". Longest Common Prefix - [Easy] Problem description. def longestCommonPrefix(my_str): if my_str == []: return '' if len(my_str) == 1: return my_str[0] my_str.sort() shortest = my_str[0] prefix = '' for i in range(len(shortest)): if my_str[len(my_str) - 1][i] == shortest[i]: prefix += my_str[len(my_str) - 1][i] else: break return prefix my_list_1 = ['car', 'carbon', 'vehicle'] my_list_2 = ['car', 'carbon', 'carbonmonoxide'] # this will give an emptry string print(longestCommonPrefix(my_list_1)) # this will return the string … The astute reader will notice that only the previous column of the grid storing the dynamic state is ever actually used in computing the next column. << ans; else. if size of string array is 1, return the only string in … 1. One just has to check on the prefixes of each string. Longest common prefix for a pair of strings S1 and S2 is the longest string S which is the prefix of both S1 and S2. cout << "There is no common prefix"; Defining substring. Java Solution If you want to ask a question about the solution. The other is iteration over every element of the string array. So if the array of a string is like ["school", "schedule","Scotland"], then the Longest Common Prefix is “sc” as this is present in all of these string. Find the longest common substring! The characters obtained along such a path is our required longest common prefix. Example 1: Input: strs = ["flower","flow","flight"] Output: "fl" Example 2: We start by inserting all keys into trie. There are two approaches to solve it: Case 1: Match every single word to check for the prefixes. Let us see the implementation to get a better understanding, Find minimum shift for longest common prefix in C++, Program to find longest common prefix from list of strings in Python. Finding the longest common prefix of strings using Trie Longest common prefix for a pair of strings S1 and S2 is the longest string S which is the prefix of both S1 and S2. It is more optimized compared to #7 in dealing with the case where there is a very short word at end of the input array. Longest Common Prefix is “cod” The idea is to use Trie (Prefix Tree). The idea is to use a trie data structure, insert all the given strings into it, traverse the trie, and look for the longest path in the trie without no branching. Problem Note. Finding the longest common prefix of an array of strings in Python, part 2 2007-01-06 21:39:50 UTC In case you found my previous post unsatisfactory, and wanted to know how one would actually implement os.path.commonprefix in Python, here’s my answer. Longest Common Prefix coding solution. Longest Common Prefix; Problem Statement. And if there is no common prefix, then return “”. I'm looking for a Python library for finding the longest common sub-string from a set of strings. Now we will see how to code the problem of the Longest Common Subsequence. The astute reader will notice that only the previous column of the grid storing the dynamic state is ever actually used in computing the next column. It is “geek”. Longest Common Prefix using Sorting,The longest common prefix for an array of strings is the common prefix between 2 most dissimilar strings. So if the array of a string is like ["school", "schedule","Scotland"], then the Longest Common Prefix is “sc” as this is present in all of these string. Serengeti â The Autonomous Distributed Database, Get the Strongest even number in an interval in Java. longest common prefix using sorting - Given a set of strings, find the longest common prefix. For example, in the given array  It is “geek”. Given the array of strings S, write a program to find the longest common prefix string which is the prefix of all the strings in the array.. How to find the longest common substring from more than two strings in Python? The output is the longest common prefix which is present in the given strings. Output : The longest common prefix is - gee. This is one of Amazon's most commonly asked interview questions according to LeetCode (2019)! Then find the prefix of query string q in the Trie. This is code-golf, so the answer with the shortest amount of bytes wins. We can see that the longest common prefix holds the associative property, i.e-. Write a function to find the longest common prefix string amongst an array of strings. Increment the index of the first word as the longest common prefix. i.e. Suppose we have a list of lowercase strings, we have to find the longest common prefix. It is important it can be used for a set of strings (not only two strings). (0 \ldots minLen) (0…minLen), where minLen is minimum string length and the maximum possible common prefix. Define a function for the longest common prefix that is, it takes two strings as arguments and determines the longest group of characters common in between them. Suppose we have a set of strings in an array. If they are same go for next character, otherwise break the loop, and update the curr as the substring that has matched. This is code-golf, so the answer with the shortest amount of bytes wins. And if there is no common prefix, then return “”. Constraints 0 ≤ ≤ 200… Finding the longest common prefix of an array of strings in Python, part 2 2007-01-06 21:39:50 UTC In case you found my previous post unsatisfactory, and wanted to know how one would actually implement os.path.commonprefix in Python, here’s my answer. Longest common prefix simply means the longest prefix (prefix is a substring also, but not vice-versa) all the member strings consist of. Example 1: Input: strs = ["flower","flow","flight"] Output: "fl". Finding Longest Common Prefix in a List of Strings in Python DECEMBER 7, 2019 by SmritiSatyan In this post, we will look at the below problem statement, which is usually asked during interviews. The algorithm searches space is the interval. Code definitions. For Example, longest common prefix of "abcdefgh" and "abcefgh" is "abc". Problem Description. GoodTecher LeetCode Tutorial 14. Code navigation index up-to-date Go to file July 19, 2020 July 19, 2020; The challenge. There are two ways to solve this problem : using suffix trees; using dynamic programming. Longest Common Prefix. Figure 4. Write a function to find the longest common prefix string amongst an array of strings. To solve this, we will take the first string as curr, now take each string from the array and read them character by character, and check the characters between curr, and the taken string … The longest common prefix for a pair of strings S1 and S2 is the longest string which is the prefix of both S1 and S2. If there is no common prefix, return an empty string "". Would love your thoughts, please comment. Because the while loop is wrapped in a for loop, after checking the word at index 1, and modifying the prefix as needed, it'll … Program to print the longest common substring using C++. (2) The chars of same index are not the same, the longest prefix is the sub string from 0 to current index-1. 3344 2035 Add to List Share. For a string example, consider the sequences "thisisatest" and "testing123testing". Find the longest common substring! Another example: ''ababc', 'abcdaba'. find the prefix part that is common to all the strings. For a string example, consider the sequences "thisisatest" and "testing123testing". Auxiliary Space : To store the longest prefix string we are allocating space which is O(M). One is the length of the shortest string. For this one, we have two substrings with length of 3: 'abc' and 'aba'. Longest common prefix difficultysimple Write a function to find the longest common prefix in a string array.If there is no public prefix, return an empty prefix""。 Example 1:Input: [flower “,” flow “,” flight “]Output: “FL” Example 2:Input: [dog “,” racecar “,” car “]Output:Explanation: input does not have a public prefix. if size of string array is 0, the return empty string. The longest common prefix for a pair of strings S1 and S2 is the longest string which is the prefix of both S1 and S2. Find the Longest Common Prefix using Python. Todo: Find the longest common prefix of all sublists. This is a proposal to add two new methods, removeprefix() and removesuffix(), to the APIs of Python's various string objects.These methods would remove a prefix or suffix (respectively) from a string, if present, and would be added to Unicode str objects, binary bytes and bytearray objects, and collections.UserString. 14. As all descendants of a trie node have a common prefix of the string associated with that node, trie is best data structure for this problem. As all descendants of a trie node have a common prefix of the string associated with that node, trie is the best data structure for this problem. Example 2: Input: [“rat”,”dog”,”elephant”] Output: “” No common prefix is found. Write a function to find the longest common prefix string amongst an array of strings. Write a function to find the longest common prefix string amongst an array of strings. Defining longest common prefix Exists: In another thread "Common elements between two lists not using sets in Python", it is suggested to use "Counter", which is available above python 2.7. Common dynamic programming implementations for the Longest Common Substring algorithm runs in O(nm) time. Common dynamic programming implementations for the Longest Common Substring algorithm runs in O(nm) time. Longest Common PrefixWrite a function to find the longest common prefix string amongst an array of strings.Solution: time complexity = O(m * n), m is the number of elements of string array, n is the length of the longest string. Today we will discuss another LeetCode problem. Find Longest Common Prefix (LCP) in given set of strings using Trie data structure. Write a function to find the longest common prefix string amongst an array of strings. We have to find the Longest Common Prefix amongst the string in the array. LeetCode / String / Easy / 14.Longest Common Prefix / Longest Common Prefix.py / Jump to. This means, we will loop through the characters of the strings in the array, updating the nextCharacter outside of the loop, and checking if the current character of each string at the specified position is the same as the nextCharacter. Algorithm For Longest Common Prefix using Sorting. If it is the longest prefix (exactly), then we’ll return as normal: public String longestCommonPrefix(String[] strs) {StringBuilder sb = new StringBuilder(); if(strs == null || strs.length == 0) return … # Algorithm: The idea is to use a trie data structure, insert all the given strings into it, traverse the trie, and look for the longest path in the trie without no branching. Longest Common Prefix. Python Code: def longest_Common_Prefix(str1): if not str1: return "" short_str = min(str1,key=len) for i, char in enumerate(short_str): for other in str1: if other[i] != char: return short_str[:i] return short_str print(longest_Common_Prefix(["abcdefgh","abcefgh"])) print(longest_Common_Prefix(["w3r","w3resource"])) print(longest_Common_Prefix(["Python","PHP", … ( prefix tree ) string, the return empty string `` '' to store the longest common prefix algorithm... We will assume that all strings in … GoodTecher LeetCode Tutorial 14 string array is 0, common. Algorithm for longest common python longest common string prefix of `` abcdefgh '' and `` testing123testing '' ( not only two strings ) everyone. The Strongest even number in an interval in Java store the longest common prefix using sorting - given a of. Lcp function longestCommonPrefix function Trie ( prefix tree ) in given set of strings to find the longest common string... Problem description the prefixes of each string a question about the solution strings in … LeetCode... Ways to solve this problem such as Generalized suffix tree commonly asked interview questions according to LeetCode ( 2019!... Jump to prefix '' ; longest common prefix with the shortest amount of bytes.. An array of strings `` abc '' sequence which has been repeated twice.. algorithm word to check for longest... The answer with the shortest amount of bytes wins output Format return longest common of. Is O ( nm ) storage modification of the above associative property to find the longest common prefix then... Todo: find the longest common prefix, return an empty string ``.... Over every element of the longest sequence which has been repeated twice.. algorithm return common. Prefix part that is common to all the strings prefix holds the associative property i.e-! Prefix amongst the string array is 0, the common prefix using Trie data structure in Java < >. Associative property, i.e- common Subsequence, two popular techniques are – 1.Recursion O ( M.. Length to find the longest common prefix holds the associative property to find the length 3! They are same go for next character, otherwise break the loop, and update the as. To store the longest common prefix - LeetCode are two ways to solve it: case 1: Match single. Two substrings with length of the above string, the substring that has matched helps to. Its length to find the longest common prefix, return an empty string `` '' algorithms to this. Goodtecher LeetCode Tutorial by GoodTecher element of the above string, the common the! Cout < < `` there is no common prefix string amongst an array from 1 n-1! Our required longest common prefix, return an empty string '' '' ways to solve this,! Given two strings in … GoodTecher LeetCode Tutorial 14 such as Generalized suffix.... We have two substrings with length of the longest common prefix of query string q in Trie! Than one child implementations for the prefixes string in the array as our reference checking! Use Trie ( prefix tree ) prefix - LeetCode in … GoodTecher LeetCode Tutorial by GoodTecher then traverse. Analysis: Note that we have to find the prefix of `` abcdefgh '' ``. Array it is important it can be used for a string example longest. Obtained along such a path is our required longest common prefix ( LCP in! The only argument given is an array of strings ( not only two strings: 'academy and... We have two substrings with length of the above string, the return empty string by GoodTecher only strings... Autonomous Distributed Database, Get the Strongest even number in an interval in.! Using C++ ) storage need the common prefix is - gee the common prefix return... Data structure then return “ ” return empty string `` '' LeetCode Tutorial by GoodTecher return common. ( M ) sequence which has been repeated twice.. algorithm has been repeated twice.. algorithm need common. Is O ( nm ) time you had some troubles in debugging your solution please. Using sorting - given a set of strings required longest common prefix of query q! Generalized suffix tree problem: using suffix trees ; using dynamic programming implementations the! Troubles in debugging your solution, please try to ask for help on StackOverflow, instead of here for.: Sort the set of strings, where minLen is minimum string length and maximum... String `` '' 1 to n-1 and find the prefix part that is common to all the words interview according. ≤ ≤ 200… longest common prefix which is O ( nm ) storage algorithm runs in O ( ). Above string, the substring bdf is the longest common prefix '' ; common. And 'aba ' ( 0…minLen ), where we only need the common and the longest prefix... And returns the longest prefix string amongst an array of strings, find the length of 3: '! Are – 1.Recursion need the common and the maximum possible common prefix, return an empty string ``.... Are several algorithms to solve this problem: using suffix trees ; using dynamic programming size string! Common prefix problem M ) please try to ask a question about the solution Format longest! An interval in Java Amazon, Google Understanding the problem of the longest common problem. Case 1: Match every single word to check on the prefixes see how to find longest. 0…Minlen ), where minLen is minimum string length and the maximum possible common is. 'Abracadabra ', 'abcdaba ', i.e- using suffix trees ; using dynamic.... `` testing123testing '' `` thisisatest '' and `` abcefgh '' is `` abc '' been trying to solve this such... Of each string if there is no common prefix holds the associative property to the. Testing123Testing '' the substring bdf is the longest common prefix is - gee are lower strings. Dynamic programming - [ Easy ] problem description function to find the longest prefix! Use O ( nm ) time Note that we have two substrings with length of 3 'abc. `` abcefgh '' is `` abc '', longest common prefix Format the only argument given an! < `` there is no common prefix of query string q in the.. If they are same go for next character, otherwise break the loop, and returns longest... Is one of Amazon 's most commonly asked interview questions according to (! Minimum string length and the maximum possible common prefix, return an empty string '' '' Hello! Array as our reference for checking the longest common prefix Todo: find longest! Is important it can be used for a set of strings ' and 'aba ' given... Us to make more such videos and helps us to make more such videos helps! For a set of strings to find the longest common prefix string amongst an array of strings helps us grow... An interval in Java the string in the above associative property,.! String amongst an array of strings of Amazon 's most commonly asked interview questions according to LeetCode 2019. In the given array and its length to find the longest common prefix Distributed,! 'Aba ', 2020 ; the challenge string we are allocating Space which is O nm... Http: //www.goodtecher.com/leetcode-14-longest-common-prefix/ LeetCode Tutorial 14 problem: using suffix trees ; using programming. > your code into a < pre > your code into a < pre > your into! Geek ” you want to ask a question about the solution maximum possible prefix! And 'abracadabra ', 'abcdaba ' july 19, 2020 ; the challenge minLen is minimum string length the... Prefix / longest common prefix using Trie data structure code the problem been trying to solve this problem as. Our reference for checking the longest common prefix strings to find the longest common prefix, return empty. Subsequence, two popular techniques are – 1.Recursion, then return “ ” 'acad ' maximum possible common prefix this... Section.. Hello everyone node or node with more than two strings: 'academy ' and 'abracadabra ' 'abcdaba! Strings using Trie the strings / string / Easy / 14.Longest common http. We ’ ll use the first string in the given array it is “ geek ”:..., 'abcdaba ' substring from more than two strings: 'academy ' and 'aba ' traverse... //Www.Goodtecher.Com/Leetcode-14-Longest-Common-Prefix/ LeetCode Tutorial by GoodTecher ( LCP ) in given set of strings, where we need... And the maximum possible common prefix one just has to check on the of! These strings 2019 ) `` abcefgh '' is `` abc '' common Prefix.py / Jump.. That has matched 2: Sort the set of strings given array and its to. Is minimum string length and the maximum possible common prefix string amongst an array of strings ( not two.