1. Two Sum
easyAsked at CoupangFind two indices in an array whose values sum to a target — Coupang uses this as a warm-up to test hash-map fluency before pivoting to inventory pricing problems.
By Sam K., Founder, InterviewChamp.AI · Last verified
Problem
Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target. Each input has exactly one solution and you may not use the same element twice.
Constraints
2 <= nums.length <= 10^4-10^9 <= nums[i] <= 10^9Only one valid answer exists
Examples
Example 1
Input
nums = [2,7,11,15], target = 9Output
[0,1]Example 2
Input
nums = [3,2,4], target = 6Output
[1,2]Approaches
1. Brute force
Check every pair with nested loops.
- Time
- O(n^2)
- Space
- O(1)
for (let i=0;i<nums.length;i++)
for (let j=i+1;j<nums.length;j++)
if (nums[i]+nums[j]===target) return [i,j];Tradeoff:
2. Hash map
Store complements in a map as you scan. One pass.
- Time
- O(n)
- Space
- O(n)
function twoSum(nums, target) {
const seen = new Map();
for (let i = 0; i < nums.length; i++) {
const need = target - nums[i];
if (seen.has(need)) return [seen.get(need), i];
seen.set(nums[i], i);
}
return [];
}Tradeoff:
Coupang-specific tips
Coupang interviewers expect you to mention that the hash-map pattern is reused for SKU-to-warehouse lookups in their inventory layer.
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