[leedcode 202] 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

  public class Solution {
      public boolean isHappy(int n) {
          //用一个set记录所有计算过的n，若出现重复（循环），返回false，若n为1，返回true;
          Set<Integer> set=new HashSet<Integer>();
          while(n!=1){
              int sum=0;
              while(n!=0){
                  sum+=(n%10)*(n%10);
                  n/=10;
              }
              if(set.contains(sum)) return false;
              set.add(sum);
              n=sum;
          }
          return true;
      }
  }