LeetCode-1.两数之和

中文：

给定一个整数数列，找出其中和为特定值的那两个数。

你可以假设每个输入都只会有一种答案，同样的元素不能被重用。

示例:

给定 nums = [2, 7, 11, 15], target = 9
因为 nums[0] + nums[1] = 2 + 7 = 9
所以返回 [0, 1]
英文：
Two Sum
Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].
以下是我的解答（参考了网上的答案）

class Solution:
    def twoSum(self, nums, target):
        numsMap = {}
        for i,num in enumerate(nums):
            if num not in numsMap:
                numsMap[target - num] = i #写target-num而不是num可以保证结果是第一个下标小于第二个下标
            else:
                return [numsMap[num],i]