fix: unique solution board generation

src/index.ts

@@ -5,7 +5,11 @@ export { type AnalyzeData, type Board, type Difficulty, type SolvingStep };
 
 export function generate(difficulty: Difficulty): Board {
   const { getBoard } = createSudokuInstance({ difficulty });
-  return getBoard();
+  const board = getBoard();
+  if (hasUniqueSolution(board)) {
+    return board;
+  }
+  return generate(difficulty);
 }
 
 export function analyze(Board: Board): AnalyzeData {
@@ -25,3 +29,30 @@ export function solve(Board: Board): {
   const board = solveAll();
   return { board, steps: solvingSteps };
 }
+
+export function hasUniqueSolution(Board: Board): boolean {
+  const slicedBoard = [...Board];
+  const solvingAttempts: { board: Board; steps: SolvingStep[] }[] = [];
+  let index = 0;
+  while (slicedBoard.some((item) => !Boolean(item))) {
+    if (solvingAttempts[index - 1]) {
+      const { steps } = solvingAttempts[index - 1];
+      const step = steps.find((step) => {
+        if (step.type === "value") {
+          return true;
+        }
+      });
+      if (!step) {
+        break;
+      }
+      step.updates.forEach((update) => {
+        slicedBoard[update.index] = update.filledValue;
+      });
+    }
+    solvingAttempts.push(solve(slicedBoard));
+    index++;
+  }
+  return solvingAttempts[0].board.every(
+    (item, index) => slicedBoard[index] === item,
+  );
+}

tests/sudoku.test.ts

@@ -1,4 +1,11 @@
-import { generate, analyze, solve } from "../src/index"; // Import the createSudokuInstance module (update path as needed)
+import {
+  generate,
+  analyze,
+  solve,
+  Board,
+  SolvingStep,
+  hasUniqueSolution,
+} from "../src/index"; // Import the createSudokuInstance module (update path as needed)
 import {
   EASY_SUDOKU_BOARD_FOR_TEST,
   EXPERT_SUDOKU_BOARD_FOR_TEST,
@@ -12,23 +19,25 @@ describe("sudoku-core", () => {
     it("should generate a valid easy difficulty board", () => {
       //Arrange
       const sudokuBoard = generate("easy");
+
       //Act
       const data = analyze(sudokuBoard);
 
       // Assert
       expect(data.difficulty).toBe("easy");
       expect(sudokuBoard.filter(Boolean).length).toBe(40);
+      expect(hasUniqueSolution(sudokuBoard)).toBe(true);
     });
     it("should generate a valid medium difficulty board", () => {
       //Arrange
       const sudokuBoard = generate("medium");
 
       //Act
       const data = analyze(sudokuBoard);
-
       // Assert
       expect(data.difficulty).toBe("medium");
       expect(sudokuBoard.filter(Boolean).length).toBe(30);
+      expect(hasUniqueSolution(sudokuBoard)).toBe(true);
     });
     it("should generate a valid hard difficulty board", () => {
       //Arrange
@@ -39,6 +48,7 @@ describe("sudoku-core", () => {
 
       // Assert
       expect(data.difficulty).toBe("hard");
+      expect(hasUniqueSolution(sudokuBoard)).toBe(true);
     });
     it("should generate a valid expert difficulty board", () => {
       //Arrange
@@ -49,6 +59,7 @@ describe("sudoku-core", () => {
 
       // Assert
       expect(data.difficulty).toBe("expert");
+      expect(hasUniqueSolution(sudokuBoard)).toBe(true);
     });
     it("should generate a valid master difficulty board", () => {
       //Arrange
@@ -59,23 +70,12 @@ describe("sudoku-core", () => {
 
       // Assert
       expect(data.difficulty).toBe("master");
+      expect(hasUniqueSolution(sudokuBoard)).toBe(true);
     });
   });
 
   describe("solve method", () => {
     it("should solve the board", () => {
-      //Arrange
-      const sudokuBoard = generate("expert");
-
-      //Act
-      const { board: solvedBoard } = solve(sudokuBoard);
-
-      // Assert
-      expect(solvedBoard.every((cell) => cell !== null)).toBe(true);
-    });
-  });
-  describe("solveStep method", () => {
-    it("should solve one more step", () => {
       //Arrange
       const sudokuBoard = generate("master");
       const unfilledCellsLength = sudokuBoard.filter(