文章作者：Tyan
博客：noahsnail.com  |  CSDN  |  简书

1. Description

Happy Number

2. Solution

• Version 1

class Solution {
public:
    bool isHappy(int n) {
        int m = n;
        map<int, int> sums;
        int sum = 0;
        while(sums[sum] == 0) {
            sums[sum] = 1;
            sum = 0;
            while(m) {
                int r = m % 10;
                sum += r * r;
                m = m / 10;
            }
            if(sum == 1) {
                return true;
            }
            m = sum;
        }
        return false;
    }
};

• Version 2

class Solution {
public:
    bool isHappy(int n) {
        int slow = calDigits(n);
        int fast = calDigits(slow);
        while(slow != 1 && slow != fast) {
            slow = calDigits(slow);
            fast = calDigits(fast);
            fast = calDigits(fast);
        }
        return slow == 1;
    }
    
private:
    int calDigits(int m) {
        int sum = 0;
        while(m) {
            int r = m % 10;
            sum += r * r;
            m = m / 10;
        }
        return sum;
    }
};

Reference

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