LeetCode 905: Sort Array By Parity

Meta Data

#

Difficulty: easy First Attempt: 2022-09-25

• Submissions: Wrong Answer → Accepted ×2 → Runtime Error → Accepted ×3

Approach

#

The same as LC 283 (Two Pointers Template 5): left is where the next even number goes, swapping each even number forward.

My Attempts

#

Attempt 1 did not return the array; attempt 2 used an undefined variable.

Solution

#

class Solution:
    def sortArrayByParity(self, nums: List[int]) -> List[int]:
        left = 0
        for right in range(len(nums)):
            if nums[right] % 2 == 0:
                nums[left], nums[right] = nums[right], nums[left]
                left += 1
        return nums

Complexity

#

Time O(n), space O(1).

Mistakes to Avoid

#

• This problem returns the array.

Interview Explanation

#

A write pointer swaps evens to the front in order, leaving odds behind. Time O(n), space O(1).