Add solution #289

Author: JoshCrozier

README.md

@@ -225,6 +225,7 @@
 279|[Perfect Squares](./0279-perfect-squares.js)|Medium|
 282|[Expression Add Operators](./0282-expression-add-operators.js)|Hard|
 283|[Move Zeroes](./0283-move-zeroes.js)|Easy|
+289|[Game of Life](./0289-game-of-life.js)|Medium|
 290|[Word Pattern](./0290-word-pattern.js)|Easy|
 292|[Nim Game](./0292-nim-game.js)|Easy|
 295|[Find Median from Data Stream](./0295-find-median-from-data-stream.js)|Hard|

solutions/0289-game-of-life.js

@@ -0,0 +1,59 @@
+/**
+ * 289. Game of Life
+ * https://leetcode.com/problems/game-of-life/
+ * Difficulty: Medium
+ *
+ * According to Wikipedia's article: "The Game of Life, also known simply as Life, is a cellular
+ * automaton devised by the British mathematician John Horton Conway in 1970."
+ *
+ * The board is made up of an m x n grid of cells, where each cell has an initial state: live
+ * (represented by a 1) or dead (represented by a 0). Each cell interacts with its eight neighbors
+ * (horizontal, vertical, diagonal) using the following four rules (taken from the above Wikipedia
+ * article):
+ * 1. Any live cell with fewer than two live neighbors dies as if caused by under-population.
+ * 2. Any live cell with two or three live neighbors lives on to the next generation.
+ * 3. Any live cell with more than three live neighbors dies, as if by over-population.
+ * 4. Any dead cell with exactly three live neighbors becomes a live cell, as if by reproduction.
+ *
+ * The next state of the board is determined by applying the above rules simultaneously to every
+ * cell in the current state of the m x n grid board. In this process, births and deaths occur
+ * simultaneously.
+ *
+ * Given the current state of the board, update the board to reflect its next state.
+ *
+ * Note that you do not need to return anything.
+ */
+
+/**
+ * @param {number[][]} board
+ * @return {void} Do not return anything, modify board in-place instead.
+ */
+var gameOfLife = function(board) {
+  const directions = [[1, -1], [1, 0], [1, 1], [0, -1], [0, 1], [-1, -1], [-1, 0], [-1, 1]];
+  const r = board.length;
+  const c = board[0].length;
+
+  for (let i = 0; i < r; i++) {
+    for (let j = 0; j < c; j++) {
+      let lives = 0;
+      for (const d of directions) {
+        if (d[0] + i < 0 || d[0] + i >= r || d[1] + j < 0 || d[1] + j >= c) {
+          continue;
+        } else if (board[d[0] + i][d[1] + j] === 1 || board[d[0] + i][d[1] + j] === 2) {
+          lives++;
+        }
+      }
+      if (board[i][j] === 0 && lives === 3) {
+        board[i][j] = 3;
+      } else if (board[i][j] === 1 && (lives < 2 || lives > 3)) {
+        board[i][j] = 2;
+      }
+    }
+  }
+
+  for (let i = 0; i < r; i++) {
+    for (let j = 0; j < c; j++) {
+      board[i][j] %= 2;
+    }
+  }
+};