README.md

922. Sort Array By Parity II

Given an array A of non-negative integers, half of the integers in A are odd, and half of the integers are even.

Sort the array so that whenever A[i] is odd, i is odd; and whenever A[i] is even, i is even.

You may return any answer array that satisfies this condition.

Example 1:

Input: [4,2,5,7]
Output: [4,5,2,7]
Explanation: [4,7,2,5], [2,5,4,7], [2,7,4,5] would also have been accepted.

Note:

1. 2 <= A.length <= 20000
2. A.length % 2 == 0
3. 0 <= A[i] <= 1000

Solutions (Python)

1. One Pass

class Solution:
    def sortArrayByParityII(self, A: List[int]) -> List[int]:
        e, o = 0, 1
        result = [None] * len(A)
        for n in A:
            if n % 2 == 0:
                result[e] = n
                e += 2
            else:
                result[o] = n
                o += 2
        return result

2. Two Points

class Solution:
    def sortArrayByParityII(self, A: List[int]) -> List[int]:
        j = 1
        for i in range(0, len(A), 2):
            if A[i] % 2:
                while A[j] % 2:
                    j += 2
                A[i], A[j] = A[j], A[i]
        return A