# Perfect reversible string

• Difficulty Level : Easy
• Last Updated : 05 Jul, 2022

You are given a string ‘str’, the task is to check that reverses of all possible substrings of ‘str’ are present in ‘str’ or not.

Examples:

```Input : str = "ab"
Output: "NO"
// all substrings are "a","b","ab" but reverse
// of "ab" is not present in str

Input : str = "aba"
Output: "YES"

Input : str = "abab"
Output: "NO"
// All substrings are "a", "b", "a", "b", "ab",
// "ba", "ab", "aba", "bab", "abab" but reverse of
// "abab" is not present in str```
Recommended Practice

A simple solution for this problem is to generate all possible substrings of ‘st’ and check if their reverse exist in the ‘str’ linearly.
An efficient solution for this problem is based on the fact that reverse of all substrings of ‘str’ will exist in ‘str’ if and only if the entire string ‘str’ is palindrome. We can justify this fact by considering the whole string, a reverse of it will exist only if it is palindrome. And if a string is palindrome, then all reverse of all substrings exist.

Below is implementation of above idea.

## C++

 `// C++ program to check if a string is perfect` `// reversible or nor` `#include` `using` `namespace` `std;`   `// This function basically checks if string is ` `// palindrome or not` `bool` `isReversible(string str)` `{` `     ``int` `i = 0, j = str.length()-1;`   `     ``// iterate from left and right` `     ``while` `(i < j)` `     ``{` `        ``if` `(str[i] != str[j])` `            ``return` `false``;` `        ``i++;` `        ``j--;` `     ``}` `     ``return` `true``;` `}`   `// Driver program to run the case` `int` `main()` `{` `  ``string str=``"aba"``;` `  ``if` `(isReversible(str))` `      ``cout << ``"YES"``;` `  ``else` `      ``cout << ``"NO"``;` `  ``return` `0;` `} `

## Java

 `// Java program to check` `// if a string is perfect` `// reversible or nor` `import` `java.io.*;`   `class` `GFG` `{`   `// This function basically ` `// checks if string is ` `// palindrome or not` `static` `boolean` `isReversible(String str)` `{` `    ``int` `i = ``0``, j = str.length() - ``1``;`   `    ``// iterate from` `    ``// left and right` `    ``while` `(i < j)` `    ``{` `        ``if` `(str.charAt(i) != str.charAt(j))` `            ``return` `false``;` `        ``i++;` `        ``j--;` `    ``}` `    ``return` `true``;` `}`   `// Driver Code` `public` `static` `void` `main (String[] args) ` `{` `    ``String str = ``"aba"``;` `    ``if` `(isReversible(str))` `        ``System.out.print(``"YES"``);` `    ``else` `        ``System.out.print( ``"NO"``);` `}` `}`   `// This code is contributed` `// by anuj_67.`

## Python3

 `# Python3 program to check if ` `# a string is perfect reversible or not`   `# This function basically checks ` `# if string is palindrome or not` `def` `isReversible(``str``):` `    ``i ``=` `0``; j ``=` `len``(``str``) ``-` `1``;`   `    ``# iterate from left and right` `    ``while` `(i < j):` `        ``if` `(``str``[i] !``=` `str``[j]):` `            ``return` `False``;` `        ``i ``+``=` `1``;` `        ``j ``-``=` `1``;` `    ``return` `True``;`   `# Driver Code` `str` `=` `"aba"``;` `if` `(isReversible(``str``)):` `    ``print``(``"YES"``);` `else``:` `    ``print``(``"NO"``);` `    `  `# This code is contributed by Princi Singh`

## C#

 `// C# program to check if a string ` `// is perfect reversible or nor ` `using` `System;`   `class` `GFG` `{`   `// This function basically checks if ` `// string is palindrome or not ` `public` `static` `bool` `isReversible(``string` `str)` `{` `    ``int` `i = 0, j = str.Length - 1;`   `    ``// iterate from left and right ` `    ``while` `(i < j)` `    ``{` `        ``if` `(str[i] != str[j])` `        ``{` `            ``return` `false``;` `        ``}` `        ``i++;` `        ``j--;` `    ``}` `    ``return` `true``;` `}`   `// Driver Code ` `public` `static` `void` `Main(``string``[] args)` `{` `    ``string` `str = ``"aba"``;` `    ``if` `(isReversible(str))` `    ``{` `        ``Console.Write(``"YES"``);` `    ``}` `    ``else` `    ``{` `        ``Console.Write(``"NO"``);` `    ``}` `}` `}`   `// This code is contributed ` `// by anuj_67`

## Javascript

 ``

Output

`YES`

Time complexity: O(n) where n is length of the string.
Auxiliary space: O(1)

This article is contributed by Shashank Mishra ( Gullu ). If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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