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1. Two Sum

easyAsked at GoDaddy

Find two indices in an array whose values sum to a given target.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Problem

Given an array of integers nums and an integer target, return the 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.

Constraints

  • 2 <= nums.length <= 10^4
  • -10^9 <= nums[i] <= 10^9
  • -10^9 <= target <= 10^9

Examples

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]

Approaches

1. Brute force

Check every pair (i, j) 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 single pass

Store complement->index as you walk; lookup in O(1) per element.

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:

GoDaddy-specific tips

GoDaddy interviewers favor candidates who can map the hash-map pattern to real registrar lookups, like resolving a domain to an account ID in O(1).

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