Lexicographically smallest string with given string as prefix

• Last Updated : 07 Oct, 2021

Given an array arr[] consisting of N strings and a string S if size M, the task is to find the lexicographically smallest string consisting of the string S as the prefix. If there doesn’t exist any string starting with prefix S then print “-1”.

Examples:

Input: arr[] = {“apple”, “appe”, “apl”, “aapl”, “appax”}, S = “app”
Output: appax
Explanation:
The lexicographical order of the strings consisting of “app” as the substring is {“aapl”, “apl”, “appax”, “appe”, “apple”}. The smallest lexicographic string containing is “appax”.

Input: arr[] = {“can”, “man”, “va”}, S = “van”
Output: -1

Approach: The given problem can be solved by sorting the given array of strings arr[] such that all the strings starting with prefixes S occur consecutively. Now traverse the given array of strings arr[] and when the first string whose prefix matches with S then print that string and break out of the loop. Otherwise, print “-1”.

Below is the implementation of the above approach:

C++

 `// C++ program for the above approach` `#include ``using` `namespace` `std;` `// Function to find the whether the``// string temp starts with str or not``bool` `is_prefix(string temp, string str)``{``    ``// Base Case``    ``if` `(temp.length() < str.length())``        ``return` `0;``    ``else` `{` `        ``// Check for the corresponding``        ``// characters in temp & str``        ``for` `(``int` `i = 0;``             ``i < str.length(); i++) {` `            ``if` `(str[i] != temp[i])``                ``return` `0;``        ``}``        ``return` `1;``    ``}``}` `// Function to find lexicographic smallest``// string consisting of the string str``// as prefix``string lexicographicallyString(``    ``string input[], ``int` `n, string str)``{``    ``// Sort the given array string arr[]``    ``sort(input, input + n);` `    ``for` `(``int` `i = 0; i < n; i++) {``        ``string temp = input[i];` `        ``// If the i-th string contains``        ``// given string as a prefix,``        ``// then print the result``        ``if` `(is_prefix(temp, str)) {``            ``return` `temp;``        ``}``    ``}` `    ``// If no string exists then``    ``// return "-1"``    ``return` `"-1"``;``}` `// Driver Code``int` `main()``{``    ``string arr[] = { ``"apple"``, ``"appe"``, ``"apl"``,``                     ``"aapl"``, ``"appax"` `};``    ``string S = ``"app"``;``    ``int` `N = 5;` `    ``cout << lexicographicallyString(``        ``arr, N, S);` `    ``return` `0;``}`

Java

 `// Java program for the above approach` `import` `java.util.Arrays;  ` `class` `GFG {` `    ``// Function to find the whether the``    ``// string temp starts with str or not``    ``static` `boolean` `is_prefix(String temp, String str)``    ``{``        ``// Base Case``        ``if` `(temp.length() < str.length())``            ``return` `false``;``        ``else` `{` `            ``// Check for the corresponding``            ``// characters in temp & str``            ``for` `(``int` `i = ``0``; i < str.length(); i++) {` `                ``if` `(str.charAt(i) != temp.charAt(i))``                    ``return` `false``;``            ``}``            ``return` `true``;``        ``}``    ``}` `    ``// Function to find lexicographic smallest``    ``// string consisting of the string str``    ``// as prefix``    ``static` `String lexicographicallyString(String[] input,``                                          ``int` `n, String str)``    ``{``        ``// Sort the given array string arr[]``        ``Arrays.sort(input);` `        ``for` `(``int` `i = ``0``; i < n; i++) {``            ``String temp = input[i];` `            ``// If the i-th string contains``            ``// given string as a prefix,``            ``// then print the result``            ``if` `(is_prefix(temp, str)) {``                ``return` `temp;``            ``}``        ``}` `        ``// If no string exists then``        ``// return "-1"``        ``return` `"-1"``;``    ``}` `    ``// Driver Code``    ``public` `static` `void` `main(String args[])``    ``{``        ``String[] arr = { ``"apple"``, ``"appe"``, ``"apl"``, ``"aapl"``, ``"appax"` `};``        ``String S = ``"app"``;``        ``int` `N = ``5``;` `        ``System.out.println(``            ``lexicographicallyString(arr, N, S));``    ``}``}` `// This code is contributed by AnkThon`

Python3

 `# Python 3 program for the above approach` `# Function to find the whether the``# string temp starts with str or not``def` `is_prefix(temp, ``str``):``  ` `    ``# Base Case``    ``if` `(``len``(temp) < ``len``(``str``)):``        ``return` `0``    ``else``:` `        ``# Check for the corresponding``        ``# characters in temp & str``        ``for` `i ``in` `range``(``len``(``str``)):``            ``if` `(``str``[i] !``=` `temp[i]):``                ``return` `0``        ``return` `1` `# Function to find lexicographic smallest``# string consisting of the string str``# as prefix``def` `lexicographicallyString(``input``, n, ``str``):``  ` `    ``# Sort the given array string arr[]``    ``input``.sort()` `    ``for` `i ``in` `range``(n):``        ``temp ``=` `input``[i]` `        ``# If the i-th string contains``        ``# given string as a prefix,``        ``# then print the result``        ``if` `(is_prefix(temp, ``str``)):``            ``return` `temp` `    ``# If no string exists then``    ``# return "-1"``    ``return` `"-1"` `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``    ``arr ``=` `[``"apple"``, ``"appe"``, ``"apl"``, ``"aapl"``, ``"appax"``]``    ``S ``=` `"app"``    ``N ``=` `5` `    ``print``(lexicographicallyString(arr, N, S))` `    ``# This code is contributed by ipg2016107.`

C#

 `// C# program for the above approach``using` `System;``class` `GFG {` `    ``// Function to find the whether the``    ``// string temp starts with str or not``    ``static` `bool` `is_prefix(``string` `temp, ``string` `str)``    ``{``        ``// Base Case``        ``if` `(temp.Length < str.Length)``            ``return` `false``;``        ``else` `{` `            ``// Check for the corresponding``            ``// characters in temp & str``            ``for` `(``int` `i = 0; i < str.Length; i++) {` `                ``if` `(str[i] != temp[i])``                    ``return` `false``;``            ``}``            ``return` `true``;``        ``}``    ``}` `    ``// Function to find lexicographic smallest``    ``// string consisting of the string str``    ``// as prefix``    ``static` `string` `lexicographicallyString(``string``[] input,``                                          ``int` `n, ``string` `str)``    ``{``        ``// Sort the given array string arr[]``        ``Array.Sort(input);` `        ``for` `(``int` `i = 0; i < n; i++) {``            ``string` `temp = input[i];` `            ``// If the i-th string contains``            ``// given string as a prefix,``            ``// then print the result``            ``if` `(is_prefix(temp, str)) {``                ``return` `temp;``            ``}``        ``}` `        ``// If no string exists then``        ``// return "-1"``        ``return` `"-1"``;``    ``}` `    ``// Driver Code``    ``public` `static` `void` `Main()``    ``{``        ``string``[] arr``            ``= { ``"apple"``, ``"appe"``, ``"apl"``, ``"aapl"``, ``"appax"` `};``        ``string` `S = ``"app"``;``        ``int` `N = 5;` `        ``Console.WriteLine(``            ``lexicographicallyString(arr, N, S));``    ``}``}` `// This code is contributed by ukasp.`

Javascript

 ``

Output:

`appax`

Time Complexity: O(M*K*N*log N), where K is the maximum length of the string in the array arr[].
Auxiliary Space: O(N)

Another Approach: The above approach can also be optimized by using the Trie Data Structure by inserting all the given strings in the Trie and then check for the first string that exists in the Trie having prefix S.

Time Complexity: O(M*N)
Auxiliary Space: O(N)

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