LeetCode 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: 19 is a happy number

• 12 + 92 = 82
• 82 + 22 = 68
• 62 + 82 = 100
• 12 + 02 + 02 = 1

class Solution {
    map<int, int> visited;
    bool isHappy(int n) {
        visited[n] = 1;
        int sum = 0;
        string num = to_string(n);
        for(int i=0; i<num.size(); i++)
            sum += pow(num[i]-'0',2);
        if(sum==1)
            return true;
        else if(visited[sum]==1)
            return false;
        else
            return isHappy(sum);
    }
};

还利用Floyd Dectection

int digitSquareSum(int n) {
    int sum = 0, tmp;
    while (n) {
        tmp = n % 10;
        sum += tmp * tmp;
        n /= 10;
    }
    return sum;
}

bool isHappy(int n) {
    int slow, fast;
    slow = fast = n;
    do {
        slow = digitSquareSum(slow);
        fast = digitSquareSum(fast);
        fast = digitSquareSum(fast);
    } while(slow != fast);
    if (slow == 1) return 1;
    else return 0;
}