Sort Array By Parity Solutions in C++

// Source : https://leetcode.com/problems/sort-array-by-parity/
// Author : Hao Chen
// Date   : 2019-03-26



class Solution {
public:
    bool isEven(int& x) {
        return x % 2 == 0;
    }
    vector<int> sortArrayByParity(vector<int>& A) {
        //two pointer, one from left to right, another from right to left
        // if left is odd number and right is even number, switch them
        int l=0, r=A.size()-1;
        while ( l < r ) {
            if ( !isEven(A[l]) && isEven(A[r]) ) swap(A[l], A[r]);
            if ( isEven(A[l]) ) l++;
            if ( !isEven(A[r]) ) r--;
        }
        return A;
    }
};

/// Source : https://leetcode.com/problems/sort-array-by-parity/solution/
/// Author : liuyubobobo
/// Time   : 2018-09-15

#include <iostream>
#include <vector>

using namespace std;


/// Two Pass
/// Time Complexity : O(n)
/// Space Complexity: O(n)
class Solution {
public:
    vector<int> sortArrayByParity(vector<int>& A) {

        vector<int> ret;
        for(int a: A)
            if(a % 2 == 0)
                ret.push_back(a);
        for(int a: A)
            if(a % 2)
                ret.push_back(a);
        return ret;
    }
};


int main() {

    return 0;
}

/// Source : https://leetcode.com/problems/sort-array-by-parity/solution/
/// Author : liuyubobobo
/// Time   : 2018-09-15

#include <iostream>
#include <vector>

using namespace std;


/// Sorting by custom comparator
/// Time Complexity : O(nlogn)
/// Space Complexity: O(1)
class Solution {
public:
    vector<int> sortArrayByParity(vector<int>& A) {

        sort(A.begin(), A.end(), cmp);
        return A;
    }

private:
    static bool cmp(int a, int b){
        if(a % 2 != b % 2)
            return a % 2 == 0;
        else
            return a < b;
    }
};


int main() {

    return 0;
}

/// Source : https://leetcode.com/problems/sort-array-by-parity/solution/
/// Author : liuyubobobo
/// Time   : 2018-09-15

#include <iostream>
#include <vector>

using namespace std;


/// Rearrange in place
/// Time Complexity : O(n)
/// Space Complexity: O(1)
class Solution {
public:
    vector<int> sortArrayByParity(vector<int>& A) {

        for(int i = 0; i < A.size(); i ++)
            if(A[i] % 2){
                int j = nextEven(A, i + 1);
                if(j < A.size())
                    swap(A[i], A[j]);
            }
        return A;
    }

private:
    int nextEven(const vector<int>& A, int start){

        for(int i = start; i < A.size(); i ++)
            if(A[i] % 2 == 0)
                return i;
        return A.size();
    }
};


void print_vec(const vector<int>& vec){
    for(int e: vec)
        cout << e << " ";
    cout << endl;
}

int main() {

    vector<int> nums {3, 1, 2, 4};
    print_vec(Solution().sortArrayByParity(nums));

    return 0;
}