Minimum reduce operations to covert a given string into a palindrome

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++

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// 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;
}

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Java

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// 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.

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Python3

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# 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

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C#

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// 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.

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PHP

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<?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
?>

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Output :

4

This article is contributed by Sahil Srivastava. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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Improved By : vt_m, Sam007



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