leetcode Happy Number

题目连接

https://leetcode.com/problems/happy-number/  

Happy Number

Description

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

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

class Solution {
public:
	bool isHappy(int n) {
		if (1 == n) return true;
		set<int> A;
		while (true) {
			int v = 0;
			do {
				int i = n % 10;
				v += i * i;
			} while (n /= 10);
			if (1 == v) return true;
			if (A.find(v) != A.end()) return false;
			n = v;
			A.insert(n);
		}
	}
};