Day2.java

/*Write an algorithm to determine if a number n is "happy".

A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers.

Return True if n is a happy number, and False if not.*/

class Solution {
  public boolean isHappy(int n) {
      if (n == 1 || n == 7)
          return true;
      int sum = n, x = n;

      // this loop executes till the sum of square of
      // digits obtained is not a single digit number
      while(sum > 9) {
          sum = 0;

          // this loop finds the sum of square of digits
          while (x > 0) {
              int d = x%10;
              sum += d*d;
              x/=10;
          }
          if (sum == 1)
              return true;
          x = sum;
      }
      if(sum == 7)
          return true;
      return false;
  }
}