LeetCode-1- Two Sum

Posted 2020-07-28 八行书

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.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

 

简言之，查找给定数组内两个数，使得两数和为给定的target

 

思路：

　　遍历给定数组，用一个哈希表存放已经遍历过的值，key是nums中的值，value是其位置索引。

　　对于当前遍历的nums[i]，查找哈希表中是否存在target-nums[i]，若存在，则返回二者索引，否则将(key=nums[i],value=i)放入哈希表中，继续遍历

 

时间复杂度：O(n)

 

python代码如下，已AC:

 1 class Solution(object):
 2     def twoSum(self, nums, target):
 3         """
 4         :type nums: List[int]
 5         :type target: int
 6         :rtype: List[int]
 7         """
 8         dictMap = {}
 9         for index, value in enumerate(nums):
10             if target - value in dictMap:
11                 return [dictMap[target - value] , index ]
12             dictMap[value] = index

 

 

提交结果：