https://leetcode.com/problems/pacific-atlantic-water-flow/// 其实，这道题目可以参考前面的那道：Trapping Rain Water II  // 可以看我blog上面的解法：// http://www.cnblogs.com/charlesblc/p/5920258.html// 注意Java set的操作，retainAll 交集，removeAll差集// 开始set里面放的是int[]，但是发现比较的时候，都被认为不一样，所以需要换成Block// 第一次提交还报了一个Runtime Error，因为没有考虑row或者column为0的情况public class Solution {    private class Block {        public int row;        public int col;        public int height;        public Block(int r, int c, int h) {            row = r;            col = c;            height = h;        }        public int hashCode() {            return row + col + height;        }        public boolean equals(Object obj) {            if (obj instanceof Block) {                Block bk = (Block)obj;                return bk.row == row && bk.col == col;            }            return false;        }    }    public List
     
       pacificAtlantic(int[][] matrix) {        List
      
        ret = new ArrayList
       
        ();                int r = matrix.length;        if (r == 0) {            return ret;        }        int c = matrix[0].length;        if (c == 0) {            return ret;        }        Set
        
          pSt = new HashSet
         
          ();        Set
          
            aSt = new HashSet
           
            (); Queue
            
              qe = new PriorityQueue
             
              (1, new Comparator
              
               () { @Override public int compare(Block o1, Block o2) { return o1.height - o2.height; } } ); boolean[][] visited = new boolean[r][c]; int[][] dirs = { {-1,0}, {0, 1}, {1, 0}, {0, -1}}; for (int i=0; i
               
                = r || nc < 0 || nc >= c || visited[nr][nc]) { continue; } visited[nr][nc] = true; if (matrix[nr][nc] >= bk.height) { Block nbk = new Block(nr, nc, matrix[nr][nc]); pSt.add(nbk); //System.out.printf("add pset new: %d, %d\n", tmp[0], tmp[1]); qe.offer(nbk); } } } // 重新初始化，计算atlantic qe.clear(); visited = new boolean[r][c]; for (int i=0; i
                
                 = r || nc < 0 || nc >= c || visited[nr][nc]) { continue; } visited[nr][nc] = true; if (matrix[nr][nc] >= bk.height) { Block nbk = new Block(nr, nc, matrix[nr][nc]); aSt.add(nbk); //System.out.printf("add aset new: %d, %d\n", tmp[0], tmp[1]); qe.offer(nbk); } } } //System.out.printf("pset length: %d\n", pSt.size()); //System.out.printf("aset length: %d\n", aSt.size()); pSt.retainAll(aSt); System.out.printf("set length: %d\n", pSt.size()); Iterator itr = pSt.iterator(); while (itr.hasNext()) { Block bk = (Block)itr.next(); int[] val = {bk.row, bk.col}; ret.add(val); } return ret; }}