def evens_before_odds(nums):
    left, right = 0, len(nums) - 1
    while left < right:
        while left < right and nums[left] % 2 == 0:
            left += 1
        while left < right and nums[right] % 2 != 0:
            right -= 1
        if left < right:
            nums[left], nums[right] = nums[right], nums[left]
            left += 1
            right -= 1
    return nums