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:

Input: 19
Output: true
Explanation: 
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

bool isHappy(int n) {
    unordered_set<int> st;
    int k = n;
    while (k != 1) {
        int tmp = 0;
        while (k) {
            tmp += (k % 10) * (k % 10);
            k /= 10;
        }
        k = tmp;
        if (st.count(k)) return false;
        else st.insert(k);
    }
    return k == 1;
}

// Floyd Cycle detection algorithm
int digitSquareSum(int num) {
    int sum = 0, tmp;
    while (num) {
        tmp = num % 10;
        sum += tmp * tmp;
        num /= 10;
    }
    return sum;
}
bool isHappy(int n) {
    int slow = n, fast = n;
    do {
        slow = digitSquareSum(slow);
        fast = digitSquareSum(digitSquareSum(fast));
    } while (slow != fast);
    if (slow == 1) return true;
    else return false;
}