[LeetCode202] Happy Number

Write an algorithm to determine if a number 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.

Example: 19 is a happy number

• 12 + 92 = 82
• 82 + 22 = 68
• 62 + 82 = 100
• 12 + 02 + 02 = 1
  

  Solution:

  use loop to calcuate the square sum until meet one of these two stops:

  1. sum is 1, return true

  2. sum value got before, which means there is a sum loop and will never goes to 1. return false

   

   

  public boolean isHappy(int n) {
          if(n<=0) return false;
          Set records = new HashSet<>();
          long ln = n;
          while(ln< Integer.MAX_VALUE){
              if(records.contains(ln)) return false;
              else records.add(ln);
              ln = getSquareSum(ln);
              if(ln == 1) return true;
          }
          return false;
      }
      public long getSquareSum(long n){
          long sum = 0;
          while(n!=0){
              sum+= Math.pow(n%10,2);
              n/=10;
          }
          return sum;
      }