Solving the Two Sum Problem in Rust: Brute Force vs HashMap

I’ve been diving into Rust and decided to challenge myself with some LeetCode problems. One of the first ones I tackled was the classic Two Sum problem — and, it turned out to be a great way to practice Rust basics like iterating over vectors and using HashMap. In this post, I’ll walk you through how I approached the problem first with a brute-force solution, and then optimized it using a hash map. I’ll also break down what “time complexity” really means as we go. The Problem You're given an array of integers nums and a target integer target. Your task is to: Return the indices of the two numbers such that they add up to the target. Constraints: Each input has exactly one solution. You can’t use the same element twice. You can return the answer in any order.

Apr 24, 2025 - 12:20

Solving the Two Sum Problem in Rust: Brute Force vs HashMap

I’ve been diving into Rust and decided to challenge myself with some LeetCode problems. One of the first ones I tackled was the classic Two Sum problem — and, it turned out to be a great way to practice Rust basics like iterating over vectors and using HashMap.

In this post, I’ll walk you through how I approached the problem first with a brute-force solution, and then optimized it using a hash map. I’ll also break down what “time complexity” really means as we go.

The Problem

You're given an array of integers nums and a target integer target. Your task is to:
Return the indices of the two numbers such that they add up to the target.

Constraints:

Each input has exactly one solution.
You can’t use the same element twice.
You can return the answer in any order.