905. Sort Array By Parity

🟩 Easy

Question

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

Two Pointer Approach

• Time complexity: O(n)

• Space complexity: O(1)

def sortArrayByParity(A: List[int]) -> List[int]:
    i,j = 0, 0
    while j < len(A):
        if A[i] % 2 == 0: 
            i += 1
            j += 1
        elif A[j] % 2 == 0:
            A[i], A[j] = A[j], A[i]
            i += 1
        else: 
            j += 1
    return A

Sort

• Time complexity: O(n log n)

• Space complexity: O(n) – depends on build-in implementation of sort

def sortArrayByParity(A):
    A.sort(key = lambda x: x % 2)
    return A