Add solution #37

Author: JoshCrozier

README.md

@@ -42,6 +42,7 @@
 34|[Find First and Last Position of Element in Sorted Array](./0034-find-first-and-last-position-of-element-in-sorted-array.js)|Medium|
 35|[Search Insert Position](./0035-search-insert-position.js)|Easy|
 36|[Valid Sudoku](./0036-valid-sudoku.js)|Medium|
+37|[Sudoku Solver](./0037-sudoku-solver.js)|Hard|
 38|[Count and Say](./0038-count-and-say.js)|Medium|
 39|[Combination Sum](./0039-combination-sum.js)|Medium|
 40|[Combination Sum II](./0040-combination-sum-ii.js)|Medium|

solutions/0037-sudoku-solver.js

@@ -0,0 +1,56 @@
+/**
+ * 37. Sudoku Solver
+ * https://leetcode.com/problems/sudoku-solver/
+ * Difficulty: Hard
+ *
+ * Write a program to solve a Sudoku puzzle by filling the empty cells.
+ *
+ * A sudoku solution must satisfy all of the following rules:
+ * - Each of the digits 1-9 must occur exactly once in each row.
+ * - Each of the digits 1-9 must occur exactly once in each column.
+ * - Each of the digits 1-9 must occur exactly once in each of the
+ *   9 3x3 sub-boxes of the grid.
+ * - The '.' character indicates empty cells.
+ */
+
+/**
+ * @param {character[][]} board
+ * @return {void} Do not return anything, modify board in-place instead.
+ */
+var solveSudoku = function(board) {
+  for (let i = 0; i < board.length; i++) {
+    for (let j = 0; j < board.length; j++) {
+      if (board[i][j] === '.') {
+        for (let k = 1; k < 10; k++) {
+          if (isValid(board, i, j, k.toString())) {
+            board[i][j] = k.toString();
+            const solution = solveSudoku(board);
+            if (solution !== false) {
+              return solution;
+            }
+            board[i][j] = '.';
+          }
+        }
+        return false;
+      }
+    }
+  }
+
+  return board;
+};
+
+function isValid(board, i, j, k) {
+  for (let index = 0; index < board.length; index++) {
+    if (board[i][index] === k) return false;
+    if (board[index][j] === k) return false;
+    const [x, y] = [
+      3 * Math.floor(i / 3) + Math.floor(index / 3),
+      3 * Math.floor(j / 3) + index % 3,
+    ];
+    if (board[x][y] === k) {
+      return false;
+    }
+  }
+
+  return true;
+}