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Minimum reduce operations to convert a given string into a palindrome
  • Difficulty Level : Basic
  • Last Updated : 21 May, 2021

Given a String find the minimum number of reduce operations required to convert a given string into a palindrome. In a reduce operation, we can change character to a immediate lower value. For example b can be covered to a.
Examples : 
 

Input  :  abcd  
Output :  4
We need to reduce c once
and d three times.

Input  : ccc
Output : 0

 

The idea is simple. We traverse string from left and compare characters of left half with their corresponding characters in right half. We add difference between to characters to result. 
 

C++




// CPP program to count minimum reduce
// operations to make a palindrome
#include <bits/stdc++.h>
using namespace std;
 
// Returns count of minimum character
// reduce operations to make palindrome.
int countReduce(string& str)
{
    int n = str.length();
    int res = 0;
 
    // Compare every character of first half
    // with the corresponding character of
    // second half and add difference to
    // result.
    for (int i = 0; i < n / 2; i++)
        res += abs(str[i] - str[n - i - 1]);
 
    return res;
}
 
// Driver code
int main()
{
    string str = "abcd";
    cout << countReduce(str);
    return 0;
}

Java




// Java program to count minimum reduce
// operations to make a palindrome
import java.io.*;
 
class GFG
{
    // Returns count of minimum character
    // reduce operations to make palindrome.
    static int countReduce(String str)
    {
        int n = str.length();
        int res = 0;
     
        // Compare every character of first half
        // with the corresponding character of
        // second half and add difference to
        // result.
        for (int i = 0; i < n / 2; i++)
            res += Math.abs(str.charAt(i)
                   - str.charAt(n - i - 1));
     
        return res;
    }
     
    // Driver code
    public static void main (String[] args)
    {
        String str = "abcd";
        System.out.println( countReduce(str));
             
    }
}
 
// This code is contributed by vt_m.

Python3




# python3 program to count minimum reduce
# operations to make a palindrome
 
# Returns count of minimum character
# reduce operations to make palindrome.
def countReduce(str):
 
    n = len(str)
    res = 0
 
    # Compare every character of first half
    # with the corresponding character of
    # second half and add difference to
    # result.
    for i in range(0, int(n/2)):
        res += abs( int(ord(str[i])) -
               int(ord(str[n - i - 1])) )
     
    return res
 
# Driver code
str = "abcd"
print(countReduce(str))
 
# This code is contributed by Sam007

C#




// C# program to count minimum reduce
// operations to make a palindrome
using System;
 
class GFG {
     
    // Returns count of minimum character
    // reduce operations to make palindrome.
    static int countReduce(string str)
    {
        int n = str.Length;
        int res = 0;
     
        // Compare every character of first
        // half with the corresponding
        // character of second half and
        // add difference to result.
        for (int i = 0; i < n / 2; i++)
            res += Math.Abs(str[i]
                    - str[n - i - 1]);
     
        return res;
    }
     
    // Driver code
    public static void Main ()
    {
        string str = "abcd";
        Console.WriteLine( countReduce(str));
             
    }
}
 
// This code is contributed by vt_m.

PHP




<?php
// PHP program to count minimum
// reduce operations to make a
// palindrome
 
// Returns count of minimum
// character reduce operations
// to make palindrome.
function countReduce($str)
{
    $n = strlen($str);
    $res = 0;
 
    // Compare every character
    // of first half with the
    // corresponding character
    // of second half and add
    // difference to result.
    for ($i = 0; $i < $n / 2; $i++)
        $res += abs(ord($str[$i]) -
                    ord($str[($n - $i - 1)]));
    return $res;
}
 
// Driver code
$str = "abcd";
echo countReduce($str);
 
// This code is contributed by Sam007
?>

Javascript




<script>
    // Javascript program to count minimum reduce
    // operations to make a palindrome
     
    // Returns count of minimum character
    // reduce operations to make palindrome.
    function countReduce(str)
    {
        let n = str.length;
        let res = 0;
       
        // Compare every character of first
        // half with the corresponding
        // character of second half and
        // add difference to result.
        for (let i = 0; i < parseInt(n / 2, 10); i++)
            res += Math.abs(str[i].charCodeAt() - str[n - i - 1].charCodeAt());
       
        return res;
    }
        
      let str = "abcd";
      document.write(countReduce(str));
     
</script>

Output : 
 

4

 



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