Two Sum

Problem Statement

Write a function solve that finds two numbers in a list that add up to a target value. Return a list with their indices in order. If the target cannot be made, return an empty list.

Example:
Input: [2, 7, 11, 15], target=9
Output: [0, 1]

Visualization

Number Map:

{}

Python Solution

def two_sum(nums, target):
    num_map = {}
    for i, num in enumerate(nums):
        complement = target - num
        if complement in num_map:
            return [num_map[complement], i]
        num_map[num] = i
    return []
# Example usage
nums = []
target = 9
result = two_sum(nums, target)
print(f"Input: nums = {nums}, target = {target}")
print(f"Output: {result}")