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1. Two Sum

easyAsked at Freshworks

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

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

Problem

Given an integer array nums and an integer target, return indices of the two numbers such that they add up to target. Each input has exactly one solution.

Constraints

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

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 for O(1) lookup. Single pass.

Time
O(n)
Space
O(n)
function twoSum(nums, target) {
  const seen = new Map();
  for (let i=0;i<nums.length;i++) {
    const c = target - nums[i];
    if (seen.has(c)) return [seen.get(c), i];
    seen.set(nums[i], i);
  }
}

Tradeoff:

Freshworks-specific tips

Freshworks favors clean, ticket-system-style code: think about how this would scale across multi-tenant customer data.

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