Algorithms of Logic | IAmChrisJalbert

Sudoku is more than a game—it's a perfect playground for computer science. When I set out to build Simply Sudoku™, I wanted to ensure that every puzzle was generated on-device, 100% unique, and guaranteed to be solvable with pure logic. This required moving beyond simple random placement and into the realm of formal algorithmic design.

The Core: Recursive Backtracking

At the heart of the app is a recursive backtracking algorithm. Sudoku is essentially a Constraint Satisfaction Problem (CSP). The rules are simple: no repeating numbers in a row, column, or 3x3 grid. However, the search space for a 9x9 grid is massive.

The backtracking approach works by attempting to place a number in a cell and then recursively trying to fill the rest of the board. If it hits a dead end, it "backtracks" and changes the previous number. To optimize this for mobile, I implemented Bitmasking, allowing the engine to check move validity in Constant Time (O[1]), ensuring the user experience remains fluid regardless of puzzle complexity.

Generating the Challenge

Generating a board is actually more difficult than solving one. To create a high-quality user experience, the generation process follows a two-step "Reductionist" workflow. First, we generate a "Perfect Board"—a fully solved, valid Sudoku grid using our backtracking engine with randomized seeds to ensure variety.

Then, we start the removal phase. Simply picking numbers to delete isn't enough; we must ensure that the resulting puzzle has exactly one unique solution. After every number is removed, the engine runs a dual-path solver check. This ensures that the player never feels cheated by an unsolvable or ambiguous puzzle.

Key Philosophy

"Building Simply Sudoku™ taught me that even the simplest classic games require sophisticated engineering to feel truly 'simple' to the user."

UI/UX Challenges in Logic Games

Technical logic is only half the battle. In keeping with the Simply Collection™ philosophy, I avoided the standard "floating keypad" which often obscures the board. Instead, Simply Sudoku™ uses a reactive selector that highlights active constraints (row, column, and block) to help the player's brain process logic faster.

By sticking to native Kotlin and modern Jetpack Compose, I ensured that these heavy recursive operations never cause "jank" in the UI thread. The result is a utility that feels as fast as a system-native tool.