Decrease operations to make String palindrome by incrementing prefix by 1

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Given a string S of numbers of size N, the duty is to seek out the minimal variety of operations required to alter a string into palindrome and we are able to carry out the next process on the string :

  • Select an index i (0 ≤ i < N) and for all 0 ≤ j ≤ i, set Sj = Sj + 1 (i.e. add 1 to each factor within the prefix of size i).

Observe: Whether it is inconceivable to transform S to a palindrome, print −1.

Examples:

Enter: S = “1234”
Output: 3

Rationalization: We will carry out the next operations:
Choose i=1, “1234”→”2234″
Choose i=2, “2234”→”3334″
Choose i=1, “3334”→”4334″ 
Therefore 3 variety of operations required to alter a string into palindrome.

Enter:  S = “2442”

Output: 0
Rationalization: The string is already a palindrome.

Strategy: The issue may be solved primarily based on the next remark: 

Initially examine if the string is already a palindrome or not. If it’s not a palindrome, then it may be transformed right into a palindrome provided that all the weather in the correct half of the string is bigger than those within the left half and the distinction between the characters nearer to finish is bigger or equal to the distinction between those nearer to the centre.

Observe the steps talked about under to implement the thought:

  • First set i = 0, j = N -1 and max = IntegerMaximumValue and ans = 0.
  • After that iterate a loop till j > i 
    • Verify if S[j] < S[i], whether it is true then we are able to’t change the string into palindrome and return -1.
    • In any other case, take absolutely the distinction of S[j] and S[i] and examine it with ans to seek out the utmost between them:
      • If the utmost worth is lower than absolutely the distinction of S[j] and S[i], return -1.
      • In any other case, max is absolutely the distinction between S[j] and S[i]
  • Return ans which is the minimal variety of operations required to alter a string right into a palindrome.

Under is the implementation of the above method.

Java

  

import java.io.*;

import java.util.*;

  

class GFG {

  

    

    

    public static int minOperation(String str, int n)

    {

        int j = n - 1;

        int i = 0;

        int max = Integer.MAX_VALUE;

        int ans = 0;

        whereas (j > i) {

            if (str.charAt(j) < str.charAt(i)) {

                return -1;

            }

            int ok = Math.abs(str.charAt(j) - str.charAt(i));

            ans = Math.max(ans, ok);

            if (max < ok) {

                return -1;

            }

            max = ok;

            i++;

            j--;

        }

        return ans;

    }

  

    

    public static void important(String[] args)

    {

        String S = "1234";

        int N = S.size();

  

        

        System.out.println(minOperation(S, N));

    }

}

Time Complexity: O(N) 
Auxiliary Area: O(1)

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