考前佛脚：leetcode第一弹

    def twoSum(nums, target):
        ans = []
        diff = None

        for i in range(len(nums)):
            if not ans:
                diff = target - nums[i]
            if len(ans) == 2:
                break
            if diff == nums[i] and len(ans) == 1:
                ans.append(i)
            if diff in nums and diff != nums[i] and len(ans) == 0:
                ans.append(i)
            if diff in nums and diff == nums[i]and len(ans) == 0:
                temp = nums.copy()
                temp.pop(i)
                if diff in temp:
                    ans.append(i)
        return ans