[LeetCode] Happy Number

Happy Number

Total Accepted: 35195 Total Submissions: 106936 Difficulty: Easy

 

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

Credits:
Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.

 

class Solution {
public:
    bool isHappy(int n) {
        if (n < 0) return false;
        unordered_set<int> loop;
        while (true) {
            if (n == 1) return true;
            int t = n;
            int round = 0;
            while (t > 0) {
                int p = t % 10;
                round += p * p;
                t /= 10;
            }
            
            if (loop.find(round) != loop.end()) return false;
            else loop.insert(round);
            n = round;
        }
        return true;
    }
};

这题用JS 就不好搞了，因为运算老是变成浮点数。。。思路比较简单，同样使用哈希表来监测loop。