Minimum number of moves required to make a string palindrome by incrementing all characters of the substring

In the fields of computer science and programming, it is very important to discover efficient algorithms for solving problems. An interesting problem is to identify the minimum number of operations required to convert a string into a palindrome by adding all characters in the substring. This article explores two ways of approaching this problem using the C programming language.

grammar

Before we delve into these methods, let’s define the syntax of the functions we will use −

int minMovesToMakePalindrome(string str);

algorithm

• Our goal is to minimize the number of moves when converting a string to a palindrome - this problem is solved by our algorithm through the following key stages −

• First, create two pointer variables from both sides of the string. The left pointer starts from the beginning of the string, and the right pointer starts from the end of the string.

• Continue our process as long as configuration limits allow i.e. once either pointer surpasses the other halt −

• Whenever the character values ​​are the same, continue to move the two pointers closer together. Whenever the character values ​​differ, the character value on the right is incremented (according to their difference) before doing any further operations. This increase is proportional to the difference between 'a' and 'c', so if str[right] equals 'c' and str[left] equals 'a', we increase str[right] by 2 (because 'a '-'c'=2). Update the move count accordingly.

• Once the left side is greater than the right side, the string will become a palindrome.

Method 1: Brute force cracking

In this method, we will consider all possible substrings and calculate the minimum number of moves required for each substring. Finally, we will return the minimum of all calculated moves.

Example

#include <iostream>
#include <string>
using namespace std;

int minMovesToMakePalindrome(string str) {
   int moves = 0;
   int length = str.length();

   for (int i = 0; i < length / 2; i++) {
      moves += abs(str[i] - str[length - i - 1]);
   }

   return moves;
}

int main() {
   string str = "abcde";
   int minMoves = minMovesToMakePalindrome(str);
   cout << "Minimum moves to make the string palindrome: " << minMoves << endl;

   return 0;
}

Output

Minimum moves to make the string palindrome: 6

Explanation

is translated as:

Explanation

A function called minMovesToMakePalindrome has been created that converts the input string str into a palindrome with the minimum number of moves required. We explain how it works with some step-by-step instructions:

We initialize the moves variable to 0, which is responsible for tracking the total number of moves required. - Since the length variable records the length of the input string str, our next step is to use a for loop to iterate half of the string so that the symmetric positions do not overlap. - Finally, inside this loop, abs(str[i] - str[length - i - 1]) calculates the absolute difference between the two end characters.

The calculated difference represents the number of moves required to make the characters at these positions equal. We add this difference to the move count.

After iterating through all necessary positions, we store the required total minimum number of moves in the moves variable. We return this value.

In the main function, we initialize a string str with the value "abcde". Then, we call the minMovesToMakePalindrome function, passing str as a parameter. The minimum number of moves returned is stored in the minMoves variable. Finally, we print the results to the console.

Method 2: Optimal double pointer method

This method uses two pointers to traverse from both ends of the string at the same time. With efficiency in mind, we employed a technique for converting a string into a palindrome, which involves progressively adding and matching characters from both ends of the input. This approach minimizes unnecessary operations and allows for faster conversions without compromising accuracy or functionality.

Example

#include <iostream>
#include <string>
using namespace std;

int minMovesToMakePalindrome(string str) {
   int moves = 0;
   int left = 0;
   int right = str.length() - 1;

   while (left <= right) {
      moves += abs(str[right] - str[left]);
      left++;
      right--;
   }

   return moves;
}

int main() {
   string str = "abcde";
   int minMoves = minMovesToMakePalindrome(str);
   cout << "Minimum moves to make the string palindrome: " << minMoves << endl;

   return 0;
}

Output

Minimum moves to make the string palindrome: 6

Explanation

is translated as:

Explanation

The goal of the following code example is to utilize the optimal two-pointer approach to determine the minimum number of moves required to convert a given string into a palindrome.

To achieve this, we created a function called minMovesToMakePalindrome. The function accepts a string argument and returns the total number of moves required. First, we set the variable used to count the number of moves to 0 and initialize the left and right pointers: the left pointer starts from the beginning of the input string (index 0) and the right pointer starts from the end (index str.length() - 1).

Our while loop iterates until left is greater than or equal to right to cover all elements in the string. In each iteration, we find the difference between the characters in the left and right positions by using abs(str[right] - str[left]), which represents how many moves are needed to make these two characters the same. We add this difference value to our run counter to get the total number of moves.

As we move towards the center of the input string, increment the left pointer and decrement the right pointer. Once there is no overlap between the left and right pointers, we convert the string to a palindrome.

At this point we return our count of total moves stored in 'moves'. In main() identical steps are followed as previously where we declare a new input string 'abcde' call minMovesToMakePalindrome with this argument which returns total minimum move count value that's assigned to new variable 'minMoves' before printing this value onto the console.

in conclusion

In the following text, two alternatives are presented, aiming to provide insight and potential answers to the problem of calculating the number of moves required to convert a given string into a palindrome in a substring via character operations. obstacle. One method, called the brute force method, encompasses all possible substrings, while the other method, called the optimal two-pointer method, greatly reduces the number of moves required. Coders can easily apply these mechanisms to solve similar obstacles and improve their solutions.

The above is the detailed content of Minimum number of moves required to make a string palindrome by incrementing all characters of the substring. For more information, please follow other related articles on the PHP Chinese website!