Rearrange int array to put odd number to left and even to right

双指针，左右调换。no extra memory, O(n)

class Solution:    def sepOddEven(self, nums):        if not nums or len(nums) == 0: return None        left = 0        right = len(nums) - 1        while left < right:            if nums[left] % 2 == 0:                nums[left], nums[right] = nums[right], nums[left]                right -= 1            else:                left += 1        return nums