Happy Number Solutions in C++

// Source : https://leetcode.com/problems/happy-number/
// Author : Hao Chen
// Date   : 2015-06-08


#include <stdlib.h>
#include <iostream>
#include <map>
using namespace std;

int squares(int n) {
    int result = 0;
    int sq = 0;
    for (; n>0; n/=10) {
        sq = n%10;
        result += (sq * sq);
    }
    return result;
}

bool isHappy(int n) {

    if (n==1) return true;

    map<int, bool> m;
    m[n]=true;

    while (n!=1) {
        n = squares(n);
        //cout << n << endl;
        if (m.find(n) != m.end()){
            return false;
        }
        m[n] = true;
    }

    return true;
}


int main(int argc, char** argv) 
{
    int n = 2;
    if (argc > 1){
        n = atoi(argv[1]);
    }
    cout << n << (isHappy(n) ? " is " : " isn't ") << "a happy number" << endl;
    return 0;
}

/// Source : https://leetcode.com/problems/happy-number/
/// Author : liuyubobobo
/// Time   : 2017-01-18

#include <iostream>
#include <unordered_set>

using namespace std;

/// Using HashTable
/// Time Complexity: O(logn)
/// Space Complexity: O(logn)
class Solution {
public:
    bool isHappy(int n) {

        unordered_set<int> record;
        record.insert(n);
        while(n != 1){
            n = op(n);
            if( record.find(n) == record.end() )
                record.insert(n);
            else
                return false;
        }

        return true;
    }

private:
    int op(int x){
        int res = 0;
        while(x){
            int t = x % 10;
            res += t * t;
            x /= 10;
        }
        return res;
    }
};


void print_bool(bool res){

    cout << (res ? "True" : "False") << endl;
}

int main() {

    print_bool(Solution().isHappy(19));
    // true

    return 0;
}

/// Source : https://leetcode.com/problems/happy-number/
/// Author : liuyubobobo
/// Time   : 2020-04-03

#include <iostream>

using namespace std;

/// Floyd's Cycle-Finding Algorithm
/// Time Complexity: O(logn)
/// Space Complexity: O(1)
class Solution {
public:
    bool isHappy(int n) {

        if(n == 1) return true;

        int slow = op(n); if(slow == 1) return true;
        int fast =op(slow); if(fast == 1) return true;
        while(slow != fast){
            slow = op(slow);
            fast = op(fast); if(fast == 1) return true;
            fast = op(fast); if(fast == 1) return true;
        }

        return false;
    }

private:
    int op(int x){
        int res = 0;
        while(x){
            int t = x % 10;
            res += t * t;
            x /= 10;
        }
        return res;
    }
};


void print_bool(bool res){

    cout << (res ? "True" : "False") << endl;
}

int main() {

    print_bool(Solution().isHappy(19));
    // true

    return 0;
}

/// Source : https://leetcode.com/problems/happy-number/
/// Author : liuyubobobo
/// Time   : 2020-04-03

#include <iostream>
#include <set>

using namespace std;

/// The only cycle is 4-16-37-58-89-145-42-20-4
/// Time Complexity: O(logn)
/// Space Complexity: O(1)
class Solution {
public:
    bool isHappy(int n) {

        set<int> cycle = {4, 16, 37, 58, 89, 145, 42, 20};
        while(n != 1){
            if(cycle.count(n)) return false;
            n = op(n);
        }
        return true;
    }

private:
    int op(int x){
        int res = 0;
        while(x){
            int t = x % 10;
            res += t * t;
            x /= 10;
        }
        return res;
    }
};


void print_bool(bool res){

    cout << (res ? "True" : "False") << endl;
}

int main() {

    print_bool(Solution().isHappy(19));
    // true

    return 0;
}