Formatted question description: https://leetcode.ca/all/905.html

905. Sort Array By Parity (Easy)

Given an array A of non-negative integers, return an array consisting of all the even elements of A, followed by all the odd elements of A.

You may return any answer array that satisfies this condition.

 

Example 1:

Input: [3,1,2,4]
Output: [2,4,3,1]
The outputs [4,2,3,1], [2,4,1,3], and [4,2,1,3] would also be accepted.

 

Note:

1. 1 <= A.length <= 5000
2. 0 <= A[i] <= 5000

Solution 1. STL

// OJ: https://leetcode.com/problems/sort-array-by-parity/

// Time: O(NlogN)
// Space: O(1)
class Solution {
public:
    vector<int> sortArrayByParity(vector<int>& A) {
        sort(begin(A), end(A), [](int a, int b) { return a % 2 < b % 2; });
        return A;
    }
};

Solution 2. Two Pointers

// OJ: https://leetcode.com/problems/sort-array-by-parity/

// Time: O(N)
// Space: O(1)
class Solution {
public:
    vector<int> sortArrayByParity(vector<int>& A) {
        for (int i = 0, j = A.size() - 1; i < j; ++i, --j) {
            while (i < j && A[i] % 2 == 0) ++i;
            while (i < j && A[j] % 2 != 0) --j;
            if (i < j) swap(A[i], A[j]);
        }
        return A;
    }
};

Java

class Solution {
    public int[] sortArrayByParity(int[] A) {
        if (A == null || A.length < 2)
            return A;
        int length = A.length;
        for (int i = 1; i < length; i++) {
            int num = A[i];
            if (num % 2 != 0)
                continue;
            int insertIndex = 0;
            for (int j = i - 1; j >= 0; j--) {
                if (A[j] % 2 == 0) {
                    insertIndex = j + 1;
                    break;
                } else
                    A[j + 1] = A[j];
            }
            A[insertIndex] = num;
        }
        return A;
    }
}

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