AlgoSolveoRoadmap › Stage 3: Binary Search › Pattern 13 of 53
DSA pattern guide
Binary Search — Classic
Sorted (or rotated sorted) input, find a target or a boundary, O(log n) required.
Use it when
Sorted (or rotated sorted) input, find a target or a boundary, O(log n) required.
Key idea
Keep an invariant on [lo, hi] and halve it each step. Decide which half is sorted when rotated.
Practice problems, in order
- Binary SearchEasy
- Sqrt(x)Easy
- Search Insert PositionEasy
- Search in Rotated Sorted ArrayMedium
- Find Minimum in Rotated Sorted ArrayMedium
- Find Peak ElementMedium
- Find First and Last Position of ElementMedium
- Search a 2D MatrixMedium
- Search a 2D Matrix IIMedium
How to practise this pattern
- Read the problem and look for the signal above before writing any code.
- Say the brute force out loud, with its time complexity, then ask what work it repeats.
- Apply the key idea and write the optimised version yourself.
- If you're stuck for more than 10 minutes, take one small hint, not the full solution.
- Move to the next problem only when you can explain why this pattern fits.
Stuck on one of these?
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