1. Two Sum-Python-LeetCode

1. 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].

First

目标和为target、num为遍历数组每个位置的值，index为数组的索引
将遍历过的数字所对应的index缓存在字典中，如果目标target-num出现在字典中。
则将字典中的索引和当前值的索引组成答案返回。

代码时间复杂度为O(n)

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        location = {}
        for index, num in enumerate(nums):
            if target - num in location:
                return [location[target-num], index]
            location[num] = index
        return [-1, -1]

Fastest