Minimum Number of Appends to Make a String Palindrome in C++

Problem statement

Given a string, find minimum characters to be appended to make a string palindrome.

Example

If string is abcac then we can make string palindrome by appending 2 highlighed characters i.e. abcacba

Algorithm

• Check if string is already palindrome, if yes then no need to append any characters.
• One by one remove a character from string and check whether remaining string is palindrome or not
• Repeat above process until string becomes palidrome
• Return the number of characters removed so far as a final answer

Example

#include <iostream>
#include <cstring>
using namespace std;
bool isPalindrome(char *str) {
   int n = strlen(str);
   if (n == 1) {
      return true;
   }
   int start = 0, end = n - 1;
   while (start < end) {
      if (str[start] != str[end]) {
         return false;
      }
      ++start;
      --end;
   }
   return true;
}
int requiredAppends(char *str) {
   if (isPalindrome(str)) {
      return 0;
   }
   return 1 + requiredAppends(str + 1);
}
int main() {
   char *str = "abcac";
   cout << "Characters to be appended = " << requiredAppends(str) << endl;
   return 0;
}

Output

When you compile and execute above program. It generates following output −

Characters to be appended = 2