[leetcode]1. Two Sum @ python

原题

https://leetcode.com/problems/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].

解题思路

建立一个字典, 遍历列表, 将值和索引存放到字典中, 每次读取数字num时, 检查target - num是否在字典中, 如果在, 返回对应的索引值.

时间复杂度: O(n)
空间复杂度: O(1)

代码

class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        d = dict()
        for idx, num in enumerate(nums):
            if target - num in d:
                return [d.get(target-num), idx]
            d[num] = idx