Leetcode 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

这个题我开始想着很简单= =做个递归就行了 写着写着不对劲。。。不知道怎么判断false= =。。。。

后来才发现false的情况是进入了死循环b(￣▽￣)d

public class Solution {      public boolean isHappy(int n) {          if(n<=0) return false;          long ln = n;          Set<Long> set = new HashSet<Long>();                    while(ln<=Integer.MAX_VALUE) {  //这里的Integer_MAZ_VALUE是一个常数            if(set.contains(ln) ) return false; else set.add(ln);  //注意returnfalse的情况是map里面出现了一样的数字 也就是死循环了            ln = digitSquare(ln);              if(ln == 1) return true;          }          return false;      }            private long digitSquare(long ln) {          long sum = 0;          while(ln!=0) {              sum += Math.pow(ln%10, 2);              ln /= 10;          }          return sum;      }  }