Add sudoku solver to misc.

misc/primes-sieveOfEratosthenes.js

@@ -1,7 +1,6 @@
 'use strict';
 
 function eratosthenes(n) {
-  // Eratosthenes algorithm to find all primes under n
   const array = new Array(n).fill(true), upperLimit = Math.sqrt(n), output = [];
 
   // Remove multiples of primes starting from 2, 3, 5,...

misc/solveSudoku.js

@@ -0,0 +1,72 @@
+'use strict';
+
+function solveSudoku(grid) {
+  const cell = [0, 0];
+
+  if (!findEmptyLocation(grid, cell)) return grid;
+
+  const [row, col] = cell;
+
+  for (let num = 1; num < 10; num++) {
+    if (checkSafeLocation(grid, row, col, num)) {
+      grid[row][col] = num;
+      if (solveSudoku(grid)) return grid;
+      else grid[row][col] = 0;
+    }
+  }
+
+  return null;
+}
+
+function findEmptyLocation(grid, cell) {
+  for (let row = 0; row < 9; row++) {
+    for (let col = 0; col < 9; col++) {
+      if (!grid[row][col]) {
+        cell[0] = row;
+        cell[1] = col;
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+function checkSafeLocation(grid, row, col, num) {
+  return (
+    !usedInRowOrColumn(grid, row, col, num) &&
+    !usedInBox(grid, row - row % 3, col - col % 3, num)
+  );
+}
+
+function usedInRowOrColumn(grid, row, col, num) {
+  for (let i = 0; i < 9; i++) {
+    if (grid[row][i] === num || grid[i][col] === num) {
+      return true;
+    }
+  }
+  return false;
+}
+
+function usedInBox(grid, row, col, num) {
+  for (let i = 0; i < 3; i++) {
+    for (let x = 0; x < 3; x++) {
+      if(grid[i + row][x + col] === num) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+const grid = [
+  [3, 0, 6, 5, 0, 8, 4, 0, 0],
+  [5, 2, 0, 0, 0, 0, 0, 0, 0],
+  [0, 8, 7, 0, 0, 0, 0, 3, 1],
+  [0, 0, 3, 0, 1, 0, 0, 8, 0],
+  [9, 0, 0, 8, 6, 3, 0, 0, 5],
+  [0, 5, 0, 0, 9, 0, 6, 0, 0],
+  [1, 3, 0, 0, 0, 0, 2, 5, 0],
+  [0, 0, 0, 0, 0, 0, 0, 7, 4],
+  [0, 0, 5, 2, 0, 6, 3, 0, 0]
+];
+console.log(solveSudoku(grid));

misc/sudokuValidator.js

@@ -17,8 +17,8 @@ function sudokuValidator(board) {
       if (!gridMap.has(currentGrid)) gridMap.set(currentGrid, new Set());
       const grid = gridMap.get(currentGrid);
       grid.add(cell);
-
     }
+
     if (column.size !== 9) return false;
   }
 
@@ -30,13 +30,14 @@ function sudokuValidator(board) {
 }
 
 const sudoku = [
-[5, 3, 4, 6, 7, 8, 9, 1, 2],
-[6, 7, 2, 1, 9, 5, 3, 4, 8],
-[1, 9, 8, 3, 4, 2, 5, 6, 7],
-[8, 5, 9, 7, 6, 1, 4, 2, 3],
-[4, 2, 6, 8, 5, 3, 7, 9, 1],
-[7, 1, 3, 9, 2, 4, 8, 5, 6],
-[9, 6, 1, 5, 3, 7, 2, 8, 4],
-[2, 8, 7, 4, 1, 9, 6, 3, 5],
-[3, 4, 5, 2, 8, 6, 1, 7, 9]];
+  [5, 3, 4, 6, 7, 8, 9, 1, 2],
+  [6, 7, 2, 1, 9, 5, 3, 4, 8],
+  [1, 9, 8, 3, 4, 2, 5, 6, 7],
+  [8, 5, 9, 7, 6, 1, 4, 2, 3],
+  [4, 2, 6, 8, 5, 3, 7, 9, 1],
+  [7, 1, 3, 9, 2, 4, 8, 5, 6],
+  [9, 6, 1, 5, 3, 7, 2, 8, 4],
+  [2, 8, 7, 4, 1, 9, 6, 3, 5],
+  [3, 4, 5, 2, 8, 6, 1, 7, 9]
+];
 console.log(sudokuValidator(sudoku));