java: add «407. Trapping Rain Water II»

Refactor to use attributes on the ‹Solution› class instead of passing
everything around…

URL:	https://leetcode.com/problems/trapping-rain-water-ii/
Signed-off-by: Matej Focko <me@mfocko.xyz>

java/trapping-rain-water-ii.java

@@ -1,17 +1,25 @@
 class Solution {
-  record Coord(int height, int y, int x) implements Comparable<Coord> {
-    private static boolean isValid(int width, int height, int y, int x) {
-      return y >= 0 && y < height && x >= 0 && x < width;
-    }
+  private int mapWidth = -1;
+  private int mapHeight = -1;
+  private int[][] heightMap = null;
 
-    public Coord add(int[][] heightMap, Coord other) {
+  private PriorityQueue<Coord> q = null;
+  private boolean[][] visited = null;
+
+  private boolean isValid(int y, int x) {
+    return y >= 0 && y < mapHeight && x >= 0 && x < mapWidth;
+  }
+
+  record Coord(int height, int y, int x) implements Comparable<Coord> {
+
+    public Coord add(Solution s, Coord other) {
       var nextY = y + other.y;
       var nextX = x + other.x;
-      if (!isValid(heightMap[0].length, heightMap.length, nextY, nextX)) {
+      if (!s.isValid(nextY, nextX)) {
         return null;
       }
 
-      return new Coord(Math.max(height, heightMap[nextY][nextX]), nextY, nextX);
+      return new Coord(Math.max(height, s.heightMap[nextY][nextX]), nextY, nextX);
     }
 
     @Override
@@ -25,15 +33,7 @@ class Solution {
         new Coord(0, 0, -1), new Coord(0, 0, 1), new Coord(0, -1, 0), new Coord(0, 1, 0)
       };
 
-  private void initQueue(
-      int[][] heightMap,
-      PriorityQueue<Coord> q,
-      boolean[][] visited,
-      int n,
-      int y0,
-      int x0,
-      int dy,
-      int dx) {
+  private void initQueue(int n, int y0, int x0, int dy, int dx) {
     for (int i = 0; i < n; ++i) {
       var y = y0 + i * dy;
       var x = x0 + i * dx;
@@ -44,25 +44,27 @@ class Solution {
   }
 
   public int trapRainWater(int[][] heightMap) {
-    int width = heightMap[0].length, height = heightMap.length;
-    var visited = new boolean[height][width];
+    mapWidth = heightMap[0].length;
+    mapHeight = heightMap.length;
+    this.heightMap = heightMap;
 
-    var q = new PriorityQueue<Coord>();
+    visited = new boolean[mapHeight][mapWidth];
+    q = new PriorityQueue<>();
 
     // initialize outer columns
-    initQueue(heightMap, q, visited, height, 0, 0, 1, 0);
-    initQueue(heightMap, q, visited, height, 0, width - 1, 1, 0);
+    initQueue(mapHeight, 0, 0, 1, 0);
+    initQueue(mapHeight, 0, mapWidth - 1, 1, 0);
 
     // initialize outer rows
-    initQueue(heightMap, q, visited, width, 0, 0, 0, 1);
-    initQueue(heightMap, q, visited, width, height - 1, 0, 0, 1);
+    initQueue(mapWidth, 0, 0, 0, 1);
+    initQueue(mapWidth, mapHeight - 1, 0, 0, 1);
 
     var totalVolume = 0;
     while (!q.isEmpty()) {
       var cell = q.poll();
 
       for (var dir : DIRECTIONS) {
-        var neighbor = cell.add(heightMap, dir);
+        var neighbor = cell.add(this, dir);
         if (neighbor == null || visited[neighbor.y()][neighbor.x()]) {
           continue;
         }