Leetcode刷题笔记10-两数之和

1. 题目

给定一个整数数组和一个目标值，找出数组中和为目标值的两个数。

你可以假设每个输入只对应一种答案，且同样的元素不能被重复利用。

2. 实例

给定 nums = [2, 7, 11, 15], target = 9

因为 nums[0] + nums[1] = 2 + 7 = 9
所以返回 [0, 1]

3. 解答

python3（用排列组合速度太慢，没过）

class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        length = len(nums)
        index = list(range(length))
        # for idx in range(length):     # 可能会有负数
        #     if nums[idx] > target:
        #         index.remove(idx)
        for i in itertools.combinations(index, 2):
            i_list = list(i)
            twosum = sum(nums[ele] for ele in i_list)
            if twosum == target: 
                return i_list

 python3 64ms

class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        length = len(nums)
        index = list(range(length))
        nums_dict = dict(zip(index, nums))
        nums_dict = sorted(nums_dict.items(), key=lambda x: x[1])
        new_index = [ele[0] for ele in nums_dict]
        new_nums = [ele[1] for ele in nums_dict]
        for idx in range(length):
            value = target - new_nums[idx]
            if value in new_nums:
                value_id = new_index[new_nums.index(value)]
                cur_id = new_index[idx]
                if value_id != cur_id:
                    return [cur_id, value_id]

4. 优答