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# Perfect reversible string

• Difficulty Level : Easy
• Last Updated : 08 Mar, 2023

You are given a string ‘str’, the task is to check the 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)

### Another method to find a string is perfect reversible or Not:-

You can also check the string is perfect reversible or not by checking the string is palindromic or not. 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 the method to find a palindrome of a string:-

## 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 s)` `{` `    ``// Stores the reverse of the` `    ``// string S` `    ``string p = s;` ` `  `    ``// Reverse the string P` `    ``reverse(p.begin(), p.end());` ` `  `    ``// If S is equal to P` `    ``if` `(s == p) {` `        ``// Return "Yes"` `        ``return` `true``;` `    ``}` `    ``// Otherwise` `   ``return` `false``;` `}` `// Driver program to run the case` `int` `main()` `{` `  ``string str=``"aba"``;` `  ``if` `(isReversible(str))` `      ``cout << ``"YES"``;` `  ``else` `      ``cout << ``"NO"``;` `  ``return` `0;` `} `   `//code by ksam24000`

## C#

 `//c# code` `using` `System;`   `namespace` `ConsoleApp1 {` `class` `GFG {` `    ``// Driver program to run the case` `    ``static` `void` `Main(``string``[] args)` `    ``{` `        ``string` `str = ``"aba"``;` `        ``if` `(IsReversible(str))` `            ``Console.WriteLine(``"YES"``);` `        ``else` `            ``Console.WriteLine(``"NO"``);` `    ``}` `    ``// This function basically checks if string is` `    ``// palindrome or not` `    ``static` `bool` `IsReversible(``string` `s)` `    ``{` `        ``// Stores the reverse of the` `        ``// string S` `        ``string` `p = s;`   `        ``char``[] arr = p.ToCharArray();` `        ``// Reverse the string P` `        ``Array.Reverse(arr);` `        ``p = ``new` `string``(arr);` `        ``return` `s == p;` `    ``}` `}` `}` `// code by ksam24000`

## Java

 `// Java program to check if a string is perfect` `// reversible or not` `import` `java.util.*;`   `public` `class` `Main {` `    ``// This function basically checks if string is` `    ``// palindrome or not` `    ``static` `boolean` `isReversible(String s)` `    ``{` `        ``// Stores the reverse of the string s` `        ``String p` `            ``= ``new` `StringBuilder(s).reverse().toString();`   `        ``// If s is equal to p` `        ``if` `(s.equals(p)) {` `            ``// Return "Yes"` `            ``return` `true``;` `        ``}` `        ``// Otherwise` `        ``return` `false``;` `    ``}`   `    ``// Driver program to run the case` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``String str = ``"aba"``;` `        ``if` `(isReversible(str))` `            ``System.out.println(``"YES"``);` `        ``else` `            ``System.out.println(``"NO"``);` `    ``}` `}`

## Python3

 `def` `isReversible(s):` `    ``# Stores the reverse of the string s` `    ``p ``=` `s[::``-``1``]`   `    ``# If s is equal to p` `    ``if` `s ``=``=` `p:` `        ``# Return True` `        ``return` `True` `    ``# Otherwise` `    ``return` `False`   `# Driver program to run the case` `if` `__name__ ``=``=` `"__main__"``:` `    ``str` `=` `"aba"` `    ``if` `isReversible(``str``):` `        ``print``(``"YES"``)` `    ``else``:` `        ``print``(``"NO"``)` `        `  `# This code is contributed by divyansh2212`

## Javascript

 `// JavaScript program to check if a string is perfect` `// reversible or not`   `// This function basically checks if string is` `// palindrome or not` `function` `isReversible(s) {` `// Stores the reverse of the` `// string S` `    ``let p = s.split(``""``).reverse().join(``""``);`   `// If S is equal to P` `    ``if` `(s == p) {` `        ``// Return "Yes"` `        ``return` `true``;` `    ``}` `// Otherwise` `    ``return` `false``;` `}`   `// Driver program to run the case` `let str = ``"aba"``;` `if` `(isReversible(str))` `    ``console.log(``"YES"``);` `else` `    ``console.log(``"NO"``);`

Output

`YES`

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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