DSA · Arrays / hashing · #01

Two Sum

Module 1 · difficulty 1/5·⏱ 30:00starts on first keystroke

Given an array of integers `nums` and an integer `target`, return the indices of the two numbers such that they add up to `target`. You may assume that each input has exactly one solution, and you may not use the same element twice. You can return the answer in any order.

Examples

nums = [2,7,11,15], target = 9 → [0,1] — nums[0] + nums[1] == 9
nums = [3,2,4], target = 6 → [1,2]
nums = [3,3], target = 6 → [0,1]

Stuck? Reveal an animated walkthrough of the approach.

Constraints

· 2 <= nums.length <= 10^4
· -10^9 <= nums[i] <= 10^9
· -10^9 <= target <= 10^9
· Exactly one valid answer exists.

Session phases

A · Clarify

B · Approach

C · Complexity

D · Edges

E · Code

F · Tradeoff

G · Score

Phase A — Clarify

Ask questions about input bounds, types, and edge constraints.

Ask the coach clarifying questions about the problem.

When you've covered this phase, advance to the next.