# Modify given string such that odd and even indices is lexicographically largest and smallest

• Last Updated : 29 Sep, 2021

Given a string S consisting of N lowercase alphabets, the task is to modify the given string by replacing all the characters with characters other than the current character such that the suffix string formed from odd and even indices is lexicographically largest and smallest respectively among all possible modifications of the string S.

Examples:

Output: azbz
Explanation:
Modify the given string S to “azbz”.
Now the suffixes starting at odd indices {zbz, z} are lexicographically largest among all possible replacements  of characters.
And all the suffixes starting at even indices {azbz, bz} are lexicographically smallest among all possible replacements  of characters.

Input: S = “ewdwnk”
Output: azazaz

Approach: The given problem can be solved by using the Greedy Approach. The idea is to replace all the odd indices characters with the character ‘z’ and if the character ‘z’ is present then replace it with ‘y’. Similarly, replace all the even indices characters with the character ‘a’ and if the character ‘a’ is present then replace it with ‘b’. After the above modifications, print the string S as the resultant string formed.

Below is the implementation of the above approach:

## C++

 `// C++ program for the above approach`   `#include ` `using` `namespace` `std;`   `// Function to modify the given string` `// satisfying the given criteria` `string performOperation(string S, ``int` `N)` `{` `    ``// Traverse the string S` `    ``for` `(``int` `i = 0; i < N; i++) {`   `        ``// If i is even` `        ``if` `(i % 2 == 0) {`   `            ``// If the S[i] is 'a', then` `            ``// change S[i] to 'b'` `            ``if` `(S[i] == ``'a'``) {` `                ``S[i] = ``'b'``;` `            ``}`   `            ``// Otherwise, change S[i]` `            ``// to 'a'` `            ``else` `{` `                ``S[i] = ``'a'``;` `            ``}` `        ``}` `        ``else` `{`   `            ``// If S[i] is 'z', then` `            ``// change S[i] to 'y'` `            ``if` `(S[i] == ``'z'``) {`   `                ``S[i] = ``'y'``;` `            ``}`   `            ``// Otherwise, change S[i]` `            ``// to 'z'` `            ``else` `{`   `                ``S[i] = ``'z'``;` `            ``}` `        ``}` `    ``}`   `    ``// Return the result` `    ``return` `S;` `}`   `// Driver Code` `int` `main()` `{` `    ``string S = ``"giad"``;` `    ``int` `N = S.size();` `    ``cout << performOperation(S, N);`   `    ``return` `0;` `}`

## Java

 `// Java program for the above approach` `import` `java.util.*;` `class` `GFG{`   `// Function to modify the given String` `// satisfying the given criteria` `static` `String performOperation(``char``[] S, ``int` `N)` `{` `  `  `    ``// Traverse the String S` `    ``for` `(``int` `i = ``0``; i < N; i++) {`   `        ``// If i is even` `        ``if` `(i % ``2` `== ``0``) {`   `            ``// If the S[i] is 'a', then` `            ``// change S[i] to 'b'` `            ``if` `(S[i] == ``'a'``) {` `                ``S[i] = ``'b'``;` `            ``}`   `            ``// Otherwise, change S[i]` `            ``// to 'a'` `            ``else` `{` `                ``S[i] = ``'a'``;` `            ``}` `        ``}` `        ``else` `{`   `            ``// If S[i] is 'z', then` `            ``// change S[i] to 'y'` `            ``if` `(S[i] == ``'z'``) {`   `                ``S[i] = ``'y'``;` `            ``}`   `            ``// Otherwise, change S[i]` `            ``// to 'z'` `            ``else` `{`   `                ``S[i] = ``'z'``;` `            ``}` `        ``}` `    ``}`   `    ``// Return the result` `    ``return` `String.valueOf(S);` `}`   `// Driver Code` `public` `static` `void` `main(String[] args)` `{` `    ``String S = ``"giad"``;` `    ``int` `N = S.length();` `    ``System.out.print(performOperation(S.toCharArray(), N));` `}` `}`   `// This code is contributed by shikhasingrajput`

## Python3

 `# python program for the above approach`   `# Function to modify the given string` `# satisfying the given criteria` `def` `performOperation(S, N):` `  `  `    ``# Traverse the string S` `    ``# we cannot directly change string` `    ``# because it is immutable` `    ``# so change of list of char` `    ``S ``=` `list``(S)` `    ``for` `i ``in` `range``(``0``, N):`   `                ``# If i is even` `        ``if` `(i ``%` `2` `=``=` `0``):`   `                        ``# If the S[i] is 'a', then` `                        ``# change S[i] to 'b'` `            ``if` `(S[i] ``=``=` `'a'``):` `                ``S[i] ``=` `'b'`   `                ``# Otherwise, change S[i]` `                ``# to 'a'` `            ``else``:` `                ``S[i] ``=` `'a'`   `        ``else``:`   `                        ``# If S[i] is 'z', then` `                        ``# change S[i] to 'y'` `            ``if` `(S[i] ``=``=` `'z'``):` `                ``S[i] ``=` `'y'`   `                ``# Otherwise, change S[i]` `                ``# to 'z'` `            ``else``:` `                ``S[i] ``=` `'z'`   `    ``# Return the result` `    ``# join the list of char` `    ``return` `"".join(S)`   `# Driver Code` `if` `__name__ ``=``=` `"__main__"``:` `    ``S ``=` `"giad"` `    ``N ``=` `len``(S)` `    ``print``(performOperation(S, N))` `    `  `    ``# This code is contributed by rakeshsahni`

## C#

 `// C# program for the above approach` `using` `System;` `using` `System.Collections.Generic;`   `class` `GFG{`   `// Function to modify the given string` `// satisfying the given criteria` `static` `string` `performOperation(``string` `S, ``int` `N)` `{` `  `  `    ``// Traverse the string S` `    ``for` `(``int` `i = 0; i < N; i++) {`   `        ``// If i is even` `        ``if` `(i % 2 == 0) {`   `            ``// If the S[i] is 'a', then` `            ``// change S[i] to 'b'` `            ``if` `(S[i] == ``'a'``) {` `                ``S = S.Substring(0, i) + ``'b'` `+ S.Substring(i + 1);` `            ``}`   `            ``// Otherwise, change S[i]` `            ``// to 'a'` `            ``else` `{` `                ``S = S.Substring(0, i) + ``'a'` `+ S.Substring(i + 1);` `            ``}` `        ``}` `        ``else` `{`   `            ``// If S[i] is 'z', then` `            ``// change S[i] to 'y'` `            ``if` `(S[i] == ``'z'``) {` `                ``S = S.Substring(0, i) + ``'y'` `+ S.Substring(i + 1);` `            ``}`   `            ``// Otherwise, change S[i]` `            ``// to 'z'` `            ``else` `{` `               ``S = S.Substring(0, i) + ``'z'` `+ S.Substring(i + 1);` `            ``}` `        ``}` `    ``}`   `    ``// Return the result` `    ``return` `S;` `}`   `// Driver Code` `public` `static` `void` `Main()` `{` `    ``string` `S = ``"giad"``;` `    ``int` `N = S.Length;` `    ``Console.Write(performOperation(S, N));` `}` `}`   `// This code is contributed by ipg2016107.`

## Javascript

 ``

Output:

`azbz`

Time Complexity: O(N)
Auxiliary Space: O(1)

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