LeetCode

Happy Number

2015.4.22 12:39

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

Solution:

　　Dull.

Accepted code:

@@ -0,0 +1,36 @@
// 1CE, 1AC, dull
#include <unordered_set>
using namespace std;

class Solution {
public:
    bool isHappy(int n) {
        unordered_set<int> us;
        unordered_set<int>::iterator it;
        
        while (true) {
            if (n == 1) {
                break;
            }
            if (us.find(n) == us.end()) {
                us.insert(n);
            } else {
                break;
            }
            n = dsum(n);
        }
        return n == 1;
    }
private:
    int dsum(int n) {
        int s = 0;
        int d;
        while (n > 0) {
            d = n % 10;
            n /= 10;
            s += d * d;
        }
        
        return s;
    }
};