Common Interview Patterns — ELI5

Imagine you are learning to cook. At first, every recipe feels brand new. But eventually you notice something: a lot of dishes use the same basic techniques — sautéing, boiling, baking. Once you learn those techniques, new recipes feel way less scary.

Coding interviews work the same way. There are hundreds of possible questions, but most of them use the same handful of patterns. Learn the patterns, and suddenly problems that looked impossible start to feel familiar.

Here are the biggest patterns, explained like recipes:

The frequency counter. Count how many times each thing appears. Like sorting your Halloween candy into piles — “I have 5 chocolate bars, 3 gummy bears, 2 lollipops.” In code, you use a dictionary to count things.

The runner technique. Use two markers that move through a list at different speeds or from different starting points. Like two kids racing on a track — the fast one catches up to the slow one, and the point where they meet tells you something useful.

Divide and conquer. Break a big problem into smaller problems, solve the small ones, and combine the answers. Like organizing a messy room: sort the books, then the toys, then the clothes, then put everything together.

The stacking trick. Keep a pile where you always add and remove from the top. Like a stack of plates — you always grab the top one. This is great for matching brackets or tracking what you have seen recently.

The greedy grab. At each step, make the choice that looks best right now. Like choosing the biggest piece of cake each time. It does not always give the perfect answer, but for many problems it does.

The beautiful thing is that there are only about 10-15 of these patterns. Once you can recognize which pattern a problem needs, you are halfway to solving it.

One thing to remember: Interview problems are not about being a genius. They are about pattern recognition — spotting which recipe to use for which dish.