Technical Interview Cheat Sheet (2026)

Coding Interviews

Technical Interview Cheat Sheet (2026)

By Ntro.io · Updated June 2026 · 6 min read

This technical interview cheat sheet is a quick reference you can skim the night before a round. It covers the patterns that show up again and again, the Big-O facts you'll be asked about, a short pre-interview checklist, and the lines to say out loud while you code. Bookmark it.

Key takeaways

Most problems are a handful of recurring patterns - recognizing the pattern is half the work.
Master five core patterns: two pointers, sliding window, hash maps/sets, BFS/DFS, and recursion/backtracking.
Keep six Big-O classes in your head, from O(1) to O(2ⁿ).
Run a quick pre-interview checklist and warm up before the round.
Interviewers grade how you think - narrate your reasoning out loud.

What this is

Most coding interview problems are not new. They're a handful of patterns wearing different clothes. If you can recognize the pattern, you've done half the work. Here's the short list, with the signal that tells you to reach for each one.

The core patterns

Two pointers

Use when: the input is sorted, or you're checking pairs from both ends (palindromes, pair sums, merging).

How: one pointer at the start, one at the end. Move them toward each other based on a comparison.
Cost: usually O(n) time, O(1) extra space.

Sliding window

Use when: you want the longest/shortest/best contiguous subarray or substring.

How: grow the window with a right pointer, shrink it with a left pointer when a rule breaks.
Cost: O(n) instead of the O(n²) brute force.

Hash maps and sets

Use when: you need fast lookups, counting, or "have I seen this before?"

How: trade memory for speed. A set turns an O(n) scan into an O(1) check.
Cost: O(1) average lookup, O(n) space.

BFS and DFS

Use when: the problem is a tree, a graph, or a grid.

BFS: trade memory for speed. A set turns an O(n) scan into an O(1) check.
DFS: uses recursion or a stack, goes deep first, good for connected components and cycle checks.
Cost: O(V + E) for a graph with V nodes and E edges.

Recursion and backtracking

Use when: you need every permutation, combination, or subset.

How: make a choice, recurse, then undo the choice and try the next one.
Watch out: always state your base case first, or you'll loop forever.

Practice out loud before the real thing

Structure is the first thing to slip once the pressure is on. The fix is simple: rehearse your STAR stories out loud beforehand and get feedback on whether they're clear. Ntro.io is an AI tool that helps you practice interviews and sharpen your answers, and it's rated 4.8 ★ on the Chrome Web Store. Use it to prepare — then tell the stories in your own words.

Practice your PM interview

The takeaway

STAR won't write your stories for you, but it will make sure your best ones land. Pick four or five experiences, run each through Situation, Task, Action, and Result, and attach a number to every result. Do that, and the behavioral round turns from the part you dread into the part you're glad they asked about.

Ntro.io helps job seekers prepare for and practice interviews with real-time AI feedback.