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1. Two Sum

easyAsked at Wise

Find two indices whose values sum to a target, a daily warm-up at Wise where matching one transfer leg to another is the bread and butter.

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

Problem

Given an array of integers nums and an integer target, return indices of two numbers that add up to target. You may assume exactly one solution exists and you may not use the same element twice.

Constraints

  • 2 <= nums.length <= 10^4
  • -10^9 <= nums[i] <= 10^9
  • Only one valid answer exists

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<n;i++) for (let j=i+1;j<n;j++) if (nums[i]+nums[j]===target) return [i,j];

Tradeoff:

2. Hash map

Store complement of each value as we scan. One pass, O(n).

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:

Wise-specific tips

Wise treats this as a matching warm-up — verbalise the analogy to pairing payer/payee legs in their peer-matched FX engine.

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Output

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