Kaprekar Number - GeeksforGeeks


Kaprekar Number - GeeksforGeeks
A Kaprekar number is a number whose square when divided into two parts and such that sum of parts is equal to the original number and none of the parts has value 0. (Source : Wiki)
Given a number, the task is to check if it is Kaprekar number or not.

  1. Find square of n and count number of digits in square.
  2. Split square at different positions and see if sum of two parts in any split becomes equal to n.
bool iskaprekar(int n)
{
    if (n == 1)
       return true;
 
    // Count number of digits in square
    int sq_n = n * n;
    int count_digits = 0;
    while (sq_n)
    {
        count_digits++;
        sq_n /= 10;
    }
 
    sq_n = n*n; // Recompute square as it was changed
 
    // Split the square at different poitns and see if sum
    // of any pair of splitted numbers is equal to n.
    for (int r_digits=1; r_digits<count_digits; r_digits++)
    {
         int eq_parts = pow(10, r_digits);
 
         // To avoid numbers like 10, 100, 1000 (These are not
         // Karprekar numbers
         if (eq_parts == n)
            continue;
 
         // Find sum of current parts and compare with n
         int sum = sq_n/eq_parts + sq_n % eq_parts;
         if (sum == n)
           return true;
    }
 
    // compare with original number
    return false;
}
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