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

• 1^2 + 9^2 = 82
• 8^2 + 2^2 = 68
• 6^2 + 8^2 = 100
• 1^2 + 0^2 + 0^2 = 1

如果迭代到最后为1了，就返回true

C++（0ms）：

class Solution {
public:
    int fun(int n){
        int res = 0 ;
        while(n){
            res += pow(n%10 , 2) ;
            n /= 10 ;
        }
        return res ;
    }
    
    bool isHappy(int n) {
        bool flag[1000] = {0} ;
        n = fun(n) ;
        while(!flag[n]){
            flag[n] = true ;
            if (n == 1)
                return true ;
            n = fun(n) ;
        }
        return false ;
    }
};