21. 调整数组顺序使奇数位于偶数前面

1. 考虑相对位置不变

• 注意要保持数组的稳定性
• 当数字为偶数时，把该数字接到列表的后面

class Solution:
    def reOrderArray(self, array):
        # write code here
        i = 0
        move = 0
        while i + move < len(array):
            if array[i] % 2 == 0:
                num = array.pop(i)
                array.append(num)
                move += 1
                i -= 1
            i += 1
        return array

2. 无需考虑相对位置不变

• 利用双指针

  class Solution:
    def exchange(self, nums: List[int]) -> List[int]:
        start = 0
        end = len(nums)-1
        while start < end:
            while nums[start]%2 == 1 and start < len(nums)-1:
                start += 1
            while nums[end]%2 == 0 and end >= 0:
                end -= 1
            if start < end:
                nums[end],nums[start] = nums[start],nums[end]
                start += 1
                end -= 1
        return nums