trapping-rain-water-ii

https://leetcode.com/problems/trapping-rain-water-ii/

// https://discuss.leetcode.com/topic/60418/java-solution-using-priorityqueue/2
// 这个解法真的好棒,真的太棒了
// 一维的也能搞定

// 利用一个PriorityQueue，从小往大排的

import java.util.Comparator;
import java.util.PriorityQueue;

public class Solution {

    public class Cell {
        int row;
        int col;
        int height;
        public Cell(int r, int c, int h) {
            row = r;
            col = c;
            height = h;
        }
    }

    public int trapRainWater(int[][] heightMap) {
        if (heightMap == null || heightMap.length == 0 || heightMap[0].length == 0) {
            return 0;
        }
        int rows = heightMap.length;
        int cols = heightMap[0].length;
        boolean [][]visited = new boolean[rows][cols];

　　　　　// 注意，是从小往大排
        PriorityQueue<Cell> pq = new PriorityQueue<Cell>(1, new Comparator<Cell>(){
            public int compare(Cell a, Cell b) {
                return a.height - b.height;
            }
        });

        for (int i=0; i<rows; i++) {
            visited[i][0] = true;
            visited[i][cols-1] = true;
            pq.offer(new Cell(i, 0, heightMap[i][0]));
            pq.offer(new Cell(i, cols-1, heightMap[i][cols-1]));
        }

        for (int i=0; i<cols; i++) {
            visited[0][i] = true;
            visited[rows-1][i] = true;
            pq.offer(new Cell(0, i, heightMap[0][i]));
            pq.offer(new Cell(rows-1, i, heightMap[rows-1][i]));
        }

        int result = 0;
        int [][]dirs = {{-1, 0}, {0, 1}, {1, 0}, {0, -1}};
        while (!pq.isEmpty()) {
            Cell cl = pq.poll();
            for (int i=0; i<4; i++) {
                int r = cl.row + dirs[i][0];
                int c = cl.col + dirs[i][1];
                if (r < 0 || r >= rows || c < 0 || c >= cols || visited[r][c]) {
                    continue;
                }
                int newHt = heightMap[r][c];
                if (heightMap[r][c] < cl.height) {
                    result += cl.height - heightMap[r][c];
                    newHt = cl.height;
                }
                pq.offer(new Cell(r, c, newHt));
                visited[r][c] = true;
            }

        }

        return result;
    }
}