# Make the string lexicographically smallest and non palindromic by replacing exactly one character

Given a palindromic string str containing only lowercase letters, the task is to print the lexicographically smallest string, by replacing exactly one character, such the string is not a palindrome.

Examples:

Input: str = “abccba”
Output: “aaccba”
Explanation:
Lexicographically smallest non-palindromic string possible is “aaccba”, here we have replaced the second letter ‘b’ by an ‘a’ which makes it a non palindrome.

Input: str = “a”
Output: -1
Explanation:
A single character is always a palindrome hence we cannot replace the value. Therefore the output is -1.

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: To solve the problem mentioned above we will check only half of the string and replace all characters which are not ‘a’ to the character ‘a’ itself. The edge case for the question is if there is only one character, we will return an empty string. Otherwise, if all the characters are the same then we will replace the last character only with character ‘b’.

Below is the implementation of the above approach:

 `// C++ program to make the string ` `// lexicographically smallest non ` `// palindromic string by replacing ` `// exactly one character ` ` `  `#include ` `using` `namespace` `std; ` ` `  `// Function to find the required string ` `string findStr(string S) ` `{ ` `    ``// length of the string ` `    ``int` `n = S.size(); ` ` `  `    ``// Iterate till half of the string ` `    ``for` `(``int` `i = 0; i < n / 2; ++i) { ` ` `  `        ``// replacing a non 'a' char with 'a' ` `        ``if` `(S[i] != ``'a'``) { ` `            ``S[i] = ``'a'``; ` ` `  `            ``return` `S; ` `        ``} ` `    ``} ` ` `  `    ``// Check if there is no 'a' in string ` `    ``// we replace last char of string by 'b' ` `    ``S[n - 1] = ``'b'``; ` ` `  `    ``// If the input is a single character ` `    ``return` `n < 2 ? ``" -1 "` `: S; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``string str = ``"a"``; ` `    ``cout << findStr(str) << endl; ` ` `  `    ``string str1 = ``"abccba"``; ` `    ``cout << findStr(str1) << endl; ` ` `  `    ``return` `0; ` `} `

 `// Java program to make the string ` `// lexicographically smallest non ` `// palindromic string by replacing ` `// exactly one character ` `import` `java.util.*; ` `class` `GFG { ` ` `  `// Function to find the required string ` `static` `String findStr(String S) ` `{ ` `    ``StringBuilder sb = ``new` `StringBuilder(S); ` ` `  `    ``// length of the string ` `    ``int` `n = sb.length(); ` ` `  `    ``// Iterate till half of the string ` `    ``for` `(``int` `i = ``0``; i < n / ``2``; ++i) ` `    ``{ ` ` `  `        ``// replacing a non 'a' char with 'a' ` `        ``if` `(sb.charAt(i) != ``'a'``)  ` `        ``{ ` `            ``sb.setCharAt(i, ``'a'``); ` ` `  `            ``return` `sb.toString(); ` `        ``} ` `    ``} ` ` `  `    ``// Check if there is no 'a' in string ` `    ``// we replace last char of string by 'b' ` `    ``sb.setCharAt(n - ``1``, ``'b'``); ` ` `  `    ``// If the input is a single character ` `    ``return` `n < ``2` `? ``" -1 "` `: sb.toString(); ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String[] args) ` `{ ` `    ``String str = ``"a"``; ` `    ``System.out.println(findStr(str)); ` ` `  `    ``String str1 = ``"abccba"``; ` `    ``System.out.println(findStr(str1)); ` `} ` `} ` ` `  `// This code is contributed by offbeat `

 `# Python3 program to make the string  ` `# lexicographically smallest non  ` `# palindromic string by replacing  ` `# exactly one character  ` ` `  `# Function to find the required string  ` `def` `findStr(S): ` `     `  `    ``S ``=` `list``(S) ` `     `  `    ``# Length of the string  ` `    ``n ``=` `len``(S) ` `     `  `    ``# Iterate till half of the string  ` `    ``for` `i ``in` `range``(``0``, n ``/``/` `2``): ` `         `  `        ``# Replacing a non 'a' char with 'a'  ` `        ``if` `S[i] !``=` `'a'``: ` `            ``S[i] ``=` `'a'` `            ``return` `(''.join(S)) ` `     `  `    ``# Check if there is no 'a' in string  ` `    ``# we replace last char of string by 'b'  ` `    ``S[n ``-` `1``] ``=` `'b'` `     `  `    ``# If the input is a single character  ` `    ``if` `n < ``2``: ` `        ``return` `'-1'` `    ``else``: ` `        ``return` `(''.join(S)) ` `     `  `# Driver Code  ` `if` `__name__``=``=``'__main__'``: ` `     `  `    ``str1 ``=` `'a'` `    ``print``(findStr(str1)) ` `     `  `    ``str2 ``=` `'abccba'` `    ``print``(findStr(str2)) ` ` `  `# This code is contributed by rutvik_56 `

 `// C# program to make the string ` `// lexicographically smallest non ` `// palindromic string by replacing ` `// exactly one character ` `using` `System; ` ` `  `class` `GFG{ ` ` `  `// Function to find the required string ` `static` `String findStr(``char` `[]S) ` `{ ` ` `  `    ``// Length of the string ` `    ``int` `n = S.Length; ` ` `  `    ``// Iterate till half of the string ` `    ``for``(``int` `i = 0; i < n / 2; ++i) ` `    ``{ ` `        `  `       ``// Replacing a non 'a' char with 'a' ` `       ``if` `(S[i] != ``'a'``) ` `       ``{ ` `           ``S[i] = ``'a'``; ` `           ``return` `new` `String(S); ` `       ``} ` `    ``} ` ` `  `    ``// Check if there is no 'a' in string ` `    ``// we replace last char of string by 'b' ` `    ``S[n - 1] = ``'b'``; ` ` `  `    ``// If the input is a single character ` `    ``return` `n < 2 ? ``" -1 "` `: ``new` `String(S); ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main(String[] args) ` `{ ` `    ``String str = ``"a"``; ` `    ``Console.WriteLine(findStr(str.ToCharArray())); ` ` `  `    ``String str1 = ``"abccba"``; ` `    ``Console.WriteLine(findStr(str1.ToCharArray())); ` `} ` `} ` ` `  `// This code is contributed by 29AjayKumar `

Output:
```-1
aaccba
```

Time Complexity: O(N)

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Improved By : offbeat, rutvik_56, 29AjayKumar

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