202. Happy Number

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*1 + 9*9 = 82
8*8 + 2*2 = 68
6*6 + 8*8 = 100
1*1 + 0*0 + 0*0 = 1

Analysis:
这个博客写的很好：《[LeetCode] Happy Number 快乐数》http://www.cnblogs.com/grandyang/p/4447233.html

Source Code（C++）:

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

class Solution {
public:
    bool isHappy(int n) {
        if (n<1) {
            return false;
        }
        else {
            vector<int> v;
            v.push_back(n);
            while(n != 1) {             
                int sum = 0;
                while(n>0) {
                    sum += (n%10)*(n%10);
                    n /= 10;
                }
                n=sum;              
                if (find(begin(v), end(v), n) != end(v)) {   //之前出现过这个数，则进入无限循环
                    return false;
                }
                v.push_back(n);
            }
            return true;
        }
    }
};

int main() {
    Solution sol;
    cout << sol.isHappy(11);
    return 0;
}