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1. Two Sum

easyAsked at Tesla

Given an array of integers and a target, return the indices of two numbers that add up to the target.

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

Problem

Given an integer array nums and an integer target, return indices i and j such that nums[i] + nums[j] = 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] <= 10^9
  • Exactly one valid answer

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 single pass

Cache complements in a map; lookup is O(1).

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);
  }
}

Tradeoff:

Tesla-specific tips

Tesla autopilot warm-up — interviewers want the O(n) hash solution fast so they can pivot to a real-time sensor-fusion follow-up where cache misses and allocation cost matter.

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Output

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