Happy Number —— Leetcode

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

首先想到如果不出现1，肯定会有一个循环，在循环的时候退出就行了；

另外用一个bool型的数组存放该数字是否出现过（或者用set存也行），bool数组更快，由于最大的int整数10位的，假如是2,999,999,999，那么用762=64*12位可表示完。

下面是代码，5ms，很快：

class Solution {public:    bool isHappy(int n) {        bool h[762] = {0};        int sum = 0;        while(sum != 1)        {        sum = 0;            while(n)            {                sum += (n%10)*(n%10);                n /= 10;            }            if(h[sum]==1)                return false;            h[sum] = 1;            n = sum;        }        return true;    }};