Two Sum Variant

Problem

Given an array of integers and a target value, find two numbers whose sum equals the target.

Example

Input:
nums = [2, 7, 11, 15]
target = 9

Output:
[0, 1]
  

Approach

Use a hash map to store numbers that have already been visited. For every number, calculate target - currentNumber and check whether that value already exists in the hash map.

Complexity

Solution

def two_sum(nums, target):
    seen = {}

    for i, num in enumerate(nums):
        complement = target - num

        if complement in seen:
            return [seen[complement], i]

        seen[num] = i

    return []
  

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