Binary Search | AlgoChronicle

Step 1

Know these before you start

Tick what you already know

Concept video

Step 2

Try it on paper

5–10 minutes, no code yet

ProblemProblem statementGiven an array of integers nums sorted in ascending order, and an integer target, write a function to search target in nums. Return its index, or -1 if it doesn't exist.Read

Problem Statement

Given an array of integers nums sorted in ascending order, and an integer target, write a function to search target in nums. Return its index, or -1 if it doesn't exist.

Imported 2026-10-09 from NeetCode auto-sync (reviewed, debug prints removed).

Input / Output

Input:  nums = [-1,0,3,5,9,12], target = 9
Output: 4

Step 6

Get it accepted

All test cases pass

Step 7

Review it so it sticks

Re-solve from memory after

Solve it yourself before you look

Reading the solution first feels like progress, but it makes the next similar problem — and the interview version — much harder, because you skipped the part where you figure it out. Give it an honest 20–30 minutes. Stuck? Re-read the pattern, watch the concept video, or try the brute force first.

Hidden: approach · solution code · optimal solution

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