update

hard/407.trapping-rain-water-ii.java

@@ -0,0 +1,56 @@
+import java.util.PriorityQueue;
+
+class Solution {
+    class Grid implements Comparable<Grid> {
+        int val;
+        int y;
+        int x;
+
+        Grid(int val, int y, int x) {
+            this.val = val;
+            this.y = y;
+            this.x = x;
+        }
+
+        @Override
+        public int compareTo(Grid that) {
+            return this.val - that.val; // Don't forget the "public"
+        }
+    }
+
+    int[] dy = new int[]{0, 1, 0, -1};
+    int[] dx = new int[]{1, 0, -1, 0};
+
+    public int trapRainWater(int[][] heightMap) {
+        int m, n;
+        if ((m = heightMap.length) == 0) return 0;
+        if ((n = heightMap[0].length) == 0) return 0;
+        PriorityQueue<Grid> pq = new PriorityQueue<>();
+        boolean[][] used = new boolean[m][n];
+        for (int i = 0; i < m; i++) {
+            pq.offer(new Grid(heightMap[i][0], i, 0));
+            pq.offer(new Grid(heightMap[i][n - 1], i, n - 1));
+            used[i][0] = true;
+            used[i][n - 1] = true;
+        }
+        for (int j = 1; j < n - 1; j++) {
+            pq.offer(new Grid(heightMap[0][j], 0, j));
+            pq.offer(new Grid(heightMap[m - 1][j], m - 1, j));
+            used[0][j] = true;
+            used[m - 1][j] = true;
+        }
+        int water = 0, height = 0;
+        while (!pq.isEmpty()) {
+            Grid curr = pq.poll();
+            if (height < curr.val) height = curr.val;
+            else water += height - curr.val;
+            for (int i = 0; i < 4; i++) {
+                int ny = curr.y + dy[i], nx = curr.x + dx[i];
+                if (ny < 0 || m <= ny || nx < 0 || n <= nx || used[ny][nx]) continue;
+                pq.offer(new Grid(heightMap[ny][nx], ny, nx));
+                used[ny][nx] = true;
+            }
+        }
+        return water;
+    }
+}