Hard data structure and algorithm practice puzzle.
Given a string and a list of dictionary words, return true if the string can be split completely into dictionary words. Work through it one prefix at a time. A position is reachable if some earlier reachable position plus a dictionary word gets you there. Position 0 is always reachable. Without this table, recursion solves the same pieces over and over.
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 Document Diff Tool, a pipeline you can run and download. See every Software Engineer project.
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