001. Two Sum
Source: LeetCode #1
Difficulty: Easy
Topics: Array, Hash Map
Problem
Given an array of integers nums and an integer target, return the indices of the two numbers that add up to target.
- Each input has exactly one solution.
- You may not use the same element twice.
- Return the answer in any order.
Example 1:
Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Example 2:
Input: nums = [3,2,4], target = 6
Output: [1,2]
Constraints:
2 <= nums.length <= 10^4-10^9 <= nums[i] <= 10^9-10^9 <= target <= 10^9
Approaches
Brute Force — O(n²) time, O(1) space
Check every pair. Simple but slow for large inputs.
Hash Map — O(n) time, O(n) space
For each number, check if its complement (target - num) is already in the map.
Store each number's index as we go.
Run
go test -v ./leetcode/easy/001-two-sum/
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