202. Happy Number Java Solutin

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

Credits:
Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.

Subscribe to see which companies asked this question

 

使用hashset 来判断是否出现循环，出现循环，外层while 结束，返回false。

public class Solution {
    public boolean isHappy(int n) {
        if(n < 0) return false;
        HashSet<Integer> hs = new HashSet<Integer>();
        int sum = 0;
        while(!hs.contains(n)){
            if(n == 1){ return true;}
            hs.add(n);
            while(n!=0){
                sum += Math.pow(n%10,2);
                n /= 10;
            }
            n = sum;
            sum = 0;
        }
        return false;
    }
}