[leetcode][hash][math] Happy Number

题目：

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

class Solution {public:   bool isHappy(int n) {if (n < 0) return false;//非法输入set<int> formerNumSet;//存放已经出现过的整数while (1){int cur = 0;while (n){int digit = n % 10;cur += digit * digit;n /= 10;}if (1 == cur) return true;else if (formerNumSet.count(cur)) return false;formerNumSet.insert(cur);//将cur放入setn = cur;}}};