Add solution #63

Author: JoshCrozier

README.md

@@ -68,6 +68,7 @@
 60|[Permutation Sequence](./0060-permutation-sequence.js)|Hard|
 61|[Rotate List](./0061-rotate-list.js)|Medium|
 62|[Unique Paths](./0062-unique-paths.js)|Medium|
+63|[Unique Paths II](./0063-unique-paths-ii.js)|Medium|
 64|[Minimum Path Sum](./0064-minimum-path-sum.js)|Medium|
 65|[Valid Number](./0065-valid-number.js)|Hard|
 66|[Plus One](./0066-plus-one.js)|Easy|

solutions/0063-unique-paths-ii.js

@@ -0,0 +1,37 @@
+/**
+ * 63. Unique Paths II
+ * https://leetcode.com/problems/unique-paths-ii/
+ * Difficulty: Medium
+ *
+ * You are given an m x n integer array grid. There is a robot initially located at
+ * the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right
+ * corner (i.e., grid[m - 1][n - 1]). The robot can only move either down or right at
+ * any point in time.
+ *
+ * An obstacle and space are marked as 1 or 0 respectively in grid. A path that the
+ * robot takes cannot include any square that is an obstacle.
+ *
+ * Return the number of possible unique paths that the robot can take to reach the
+ * bottom-right corner.
+ *
+ * The testcases are generated so that the answer will be less than or equal to 2 * 109.
+ */
+
+/**
+ * @param {number[][]} grid
+ * @return {number}
+ */
+var uniquePathsWithObstacles = function(grid) {
+  const cache = new Array(grid.length).fill(0).map(v => new Array(grid[0].length).fill(0));
+
+  function traverse(x, y) {
+    if (grid[x] === undefined || grid[x][y] === undefined || grid[x][y] === 1) return 0;
+    if (x === grid.length - 1 && y === grid[0].length - 1) return 1;
+    if (!cache[x][y]) {
+      cache[x][y] = traverse(x + 1, y) + traverse(x, y + 1);
+    }
+    return cache[x][y];
+  }
+
+  return traverse(0, 0);
+};