Leetcode 1.两数之和 By Python

思路

很容易想到的方法是二重循环遍历一遍，但是会很慢

把加法变减法可以大大加速

代码

class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        book = {}
        for key,value in enumerate(nums):
            if value not in book:
                delta = target - value
                book[delta] = key		#对应的key和value分别是差值和索引
            else:
                return [book[value], key]

PS.二重循环是7000+ms，上面的代码只要40ms