Hard data structure and algorithm practice puzzle.
Given n, return how many ways you can place n queens on an n by n chessboard so no two attack each other. Place one queen per row. For each row, try every column, and skip any column or diagonal that's already taken by a queen above. Checking as you go, instead of building every board and filtering after, is what makes this finish.
Solve it three ways: snap the jigsaw pieces together, fill in the blanks, or type it from scratch against the tests. This one is free.
Every line of the solution comes with a note explaining why it is there, and a step by step replay shows the code running. At level 3, where you type it yourself, you can ask for an AI mock interview on this problem that ends with a hiring manager's scorecard.
Then grow it into a real project with the Software Engineer button: this puzzle becomes the Order Heatmap, a pipeline you can run and download. See every Software Engineer project.
Browse all 576 puzzles