2019年5月25日 开始了我的刷题之路，此笔记记录刷题流程
[LeetCode] 1. Two Sum 两数之和
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]
思路：遍历一次，遍历过程中建立字典，和减法，除法都有对称性，如果在列表中找到了目标1，根据 sum = a + b 那么后面必然还会找到一个目标2 ,
Python 代码：
1 class Solution:
2 def twoSum(self, nums: List[int], target: int) -> List[int]:
3 if nums == []:
4 return None
5 seen = {}
6
7 for index,value in enumerate(nums):
8 x = target - value
9 if x in seen:
10 return [seen[x],index]
11 else:
12 seen[value] = index
13
14
15 #EG: target = 7
16 # list = [1,2,3,4,5,]
17
18 #如果a能成功，b不在字典里，但是列表里的确有b ，不要慌，这时把a放到字典里，减法有对称性，扫描到b的时候必然能成功找到 a 在字典里，返回两个下标
[LeetCode] 1. Two Sum 两数之和
原文：https://www.cnblogs.com/Poceer/p/10922779.html
