Happy Number 博客分类： Leetcode 哈希

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

题目中规定一个happy number的规则，我们借助于哈希表存储已经出现过的数字，如果计算的结果为1我们就返回true；如果计算出的结果不为1并且哈希表中已经存在这个数，就说明了它无限循环，我们返回false。代码如下：

public class Solution {
    public boolean isHappy(int n) {
        HashSet<Integer> set = new HashSet<Integer>();
        int tem = n;
        while(true) {
            if(tem == 1) return true;
            if(set.contains(tem)) {
                return false;
            } else {
                set.add(tem);
                tem = getSquare(tem);
            }
        }
    }
    public int getSquare(int n) {
        int result = 0;
        while(n > 0) {
            result += (n % 10) * (n % 10);
            n /= 10;
        }
        return result;
    }
}