[LeetCode]1.Two Sum(Easy)

Sherlock Chiou

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Feb 19, 2021

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Description:

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example 1:

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Output: Because nums[0] + nums[1] == 9, we return [0, 1].

Solution 1:

Time complexity O(n²)

Solution 2:

Time complexity O(n), we use a hashmap to help us traverse the nums list just once. Each time we would check if the complement exists in the hashmap.