#哈希表 #快乐数

happy-number.cpp

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