The challenge

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

The solution

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class Solution {
    // return a sorted primitive int array
    public int[] sortArrayByParity(int[] A) {
        
        // keep track of place
        int lastIndex = 0;
        
        // loop through input array
        for (int i=0; i<A.length; i++) {
            // if we found an even number
            if (A[i]%2==0) {
                // keep track of the values
                int lastValue = A[lastIndex];
                int thisValue = A[i];
                
                // swap the values
                A[i] = lastValue;
                A[lastIndex] = thisValue;
                
                // increment our swap index
                lastIndex++;
            }
        }
        
        // return a sorted array
        return A;
    }
}