27. 移除元素

 

 思路见注释。

class Solution(object):
    def removeElement(self, nums, val):
        """
        :type nums: List[int]
        :type val: int
        :rtype: int
        """
        if len(nums) == 0:
            return 0
        # 双指针
        i, j = 0, len(nums) - 1
        while i < j:
            # j指向的等于val，j前移
            if nums[j] == val:
                j -= 1
                continue
            # 如果i指向的等于val，交换i和j的值，j前移
            if nums[i] == val:
                nums[i], nums[j] = nums[j], nums[i]
                j -= 1
            # i每一趟都后移
            i += 1
        print(nums, i, j)
        if nums[i] == val:
            return len(nums[:i])
        else:
            return len(nums[:i]) + 1

if __name__ == '__main__':
    solution = Solution()
    print(solution.removeElement(nums=[0, 1, 2, 2, 3, 2, 4, 2, 5], val=2))
    print(solution.removeElement(nums=[], val=5))