Add solution #407

Author: JoshCrozier

0407-trapping-rain-water-ii.js

@@ -0,0 +1,45 @@
+/**
+ * 407. Trapping Rain Water II
+ * https://leetcode.com/problems/trapping-rain-water-ii/
+ * Difficulty: Hard
+ *
+ * Given an m x n integer matrix heightMap representing the height of each unit cell in a 2D
+ * elevation map, return the volume of water it can trap after raining.
+ */
+
+/**
+ * @param {number[][]} heightMap
+ * @return {number}
+ */
+var trapRainWater = function(heightMap) {
+  const minHeap = new MinPriorityQueue({ priority: ([value]) => value });
+  const history = new Array(heightMap.length).fill(0)
+    .map(() => new Array(heightMap[0].length).fill(false));
+
+  for (let i = 0; i < heightMap.length; i++) {
+    for (let j = 0; j < heightMap[0].length; j++) {
+      if (i === 0 || i === heightMap.length - 1 || j === 0 || j === heightMap[0].length - 1) {
+        minHeap.enqueue([heightMap[i][j], i, j]);
+        history[i][j] = true;
+      }
+    }
+  }
+
+  let result = 0;
+  while (minHeap.size()) {
+    const [weight, i, j] = minHeap.dequeue().element;
+    [[0, 1], [1, 0], [0, -1], [-1, 0]].forEach(([x, y]) => {
+      const [rowIndex, columnIndex] = [i + x, j + y];
+      if (rowIndex >= 0 && rowIndex < heightMap.length && columnIndex >= 0
+          && columnIndex < heightMap[0].length && !history[rowIndex][columnIndex]) {
+        result += Math.max(0, weight - heightMap[rowIndex][columnIndex]);
+        minHeap.enqueue([
+          Math.max(weight, heightMap[rowIndex][columnIndex]), rowIndex, columnIndex
+        ]);
+        history[rowIndex][columnIndex] = true;
+      }
+    });
+  }
+
+  return result;
+};

README.md

@@ -197,6 +197,7 @@
 394|[Decode String](./0394-decode-string.js)|Medium|
 395|[Longest Substring with At Least K Repeating Characters](./0395-longest-substring-with-at-least-k-repeating-characters.js)|Medium|
 405|[Convert a Number to Hexadecimal](./0405-convert-a-number-to-hexadecimal.js)|Easy|
+407|[Trapping Rain Water II](./0407-trapping-rain-water-ii.js)|Hard|
 412|[Fizz Buzz](./0412-fizz-buzz.js)|Easy|
 414|[Third Maximum Number](./0414-third-maximum-number.js)|Easy|
 415|[Add Strings](./0415-add-strings.js)|Easy|