java version


  • 2
    C
    public class Solution {
        public int trapRainWater(int[][] heightMap) {
            class Cell{
                int x;
                int y;
                int h;
                Cell(int x, int y, int height){
                    this.x = x;
                    this.y = y;
                    h = height;
                }
            }
             if (heightMap == null || heightMap.length == 0 || heightMap[0].length == 0) {
                return 0;
            }
    
            int m = heightMap.length;
            int n = heightMap[0].length;
            PriorityQueue<Cell> pq = new PriorityQueue<>((v1,v2)->v1.h - v2.h);
             boolean[][] visited = new boolean[m][n];
            for(int i = 0; i < n; i++){
                visited[0][i] = true;
                visited[m-1][i] = true;
                pq.offer( new Cell(0, i, heightMap[0][i]));
                pq.offer(new Cell(m-1, i, heightMap[m-1][i]));
            }
            for(int i = 1; i < m-1; i++){
                visited[i][0] = true;
                visited[i][n-1] = true;
                pq.offer(new Cell(i, 0, heightMap[i][0]));
                pq.offer(new Cell(i, n-1, heightMap[i][n-1]));
            }
            int[] xs = {0,  0, 1, -1};
            int[] ys = {1, -1, 0,  0};
            int sum = 0;
            while (!pq.isEmpty()) {
                Cell cell = pq.poll();
                for (int i = 0; i < 4; i++) {
                    int nx = cell.x + xs[i];
                    int ny = cell.y + ys[i];
                    if (nx >= 0 && nx < m && ny >= 0 && ny < n && !visited[nx][ny]) {
                        visited[nx][ny] = true;
                        sum += Math.max(0, cell.h - heightMap[nx][ny]);
                        pq.offer(new Cell(nx, ny, Math.max(heightMap[nx][ny], cell.h)));
                    }
                }
            }
            return sum;
        }
    }

Log in to reply
 

Looks like your connection to LeetCode Discuss was lost, please wait while we try to reconnect.