Two Sum — Find Pair with Target
Difficulty: Easy · Topics: Array, HashMap, Searching
Difficulty: Easy | Tags: Array, HashMap, Searching
Description
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, and you may not use the same element twice.
Implement:
twoSum(nums, target) → int[2]
Examples
Example 1:
Input: nums = [2, 7, 11, 15], target = 9
Output: [0, 1]
Explanation: nums[0] + nums[1] = 2 + 7 = 9
Example 2:
Input: nums = [3, 2, 4], target = 6
Output: [1, 2]
Example 3:
Input: nums = [3, 3], target = 6
Output: [0, 1]
Constraints
2 <= nums.length <= 10^4-10^9 <= nums[i] <= 10^9-10^9 <= target <= 10^9- Exactly one valid answer exists.
Hints
Hint 1
Brute force is O(n²). Use a HashMap to store seen values → indices for O(n).
Hint 2
For each element, check if target - nums[i] is already in the map.