Add solution #790

Author: JoshCrozier

README.md

@@ -339,6 +339,7 @@
 748|[Shortest Completing Word](./0748-shortest-completing-word.js)|Easy|
 762|[Prime Number of Set Bits in Binary Representation](./0762-prime-number-of-set-bits-in-binary-representation.js)|Easy|
 784|[Letter Case Permutation](./0784-letter-case-permutation.js)|Medium|
+790|[Domino and Tromino Tiling](./0790-domino-and-tromino-tiling.js)|Medium|
 791|[Custom Sort String](./0791-custom-sort-string.js)|Medium|
 796|[Rotate String](./0796-rotate-string.js)|Easy|
 802|[Find Eventual Safe States](./0802-find-eventual-safe-states.js)|Medium|

solutions/0790-domino-and-tromino-tiling.js

@@ -0,0 +1,28 @@
+/**
+ * 790. Domino and Tromino Tiling
+ * https://leetcode.com/problems/domino-and-tromino-tiling/
+ * Difficulty: Medium
+ *
+ * You have two types of tiles: a 2 x 1 domino shape and a tromino shape. You may rotate
+ * these shapes.
+ *
+ * Given an integer n, return the number of ways to tile an 2 x n board. Since the answer
+ * may be very large, return it modulo 109 + 7.
+ *
+ * In a tiling, every square must be covered by a tile. Two tilings are different if and
+ * only if there are two 4-directionally adjacent cells on the board such that exactly
+ * one of the tilings has both squares occupied by a tile.
+ */
+
+/**
+ * @param {number} n
+ * @return {number}
+ */
+var numTilings = function(n) {
+  const MOD_VALUE = Math.pow(10, 9) + 7;
+  const dp = { 1: 1, 2: 2, 3: 5 };
+  for (let i = 4; i <= n; i++) {
+    dp[i] = (2 * dp[i - 1] + dp[i - 3]) % MOD_VALUE;
+  }
+  return dp[n];
+};