思路：
倒过来想



代码：


class Solution {
    boolean visit1[][];
    boolean visit2[][];
    public List<List<Integer>> pacificAtlantic(int[][] grid) {
        if(grid.length==0)return new ArrayList<>();
        int r=grid.length;int c=grid[0].length;
        List<List<Integer>>res=new ArrayList<>();
        visit1=new boolean[r][c];
        visit2=new boolean[r][c];
        
        for(int i=0;i<r;i++){
            dfs(grid,i,0,visit1);
        }
        
        for(int i=0;i<r;i++){
            dfs(grid,i,c-1,visit2);
        }
        
        
        for(int i=0;i<c;i++){
            dfs(grid,0,i,visit1);
        }
        
        for(int i=0;i<c;i++){
            dfs(grid,r-1,i,visit2);
        }
        
        
        
        for(int i=0;i<r;i++){
            for(int j=0;j<c;j++){
                if(visit1[i][j]&&visit2[i][j]){
                    List<Integer>l=new ArrayList<>();
                    l.add(i);l.add(j);
                    res.add(l);
                }
            }
        }
        return res;
    }
    
    public void dfs(int grid[][],int r,int c,boolean visit[][]){
        if(visit[r][c])return;
        int cur=grid[r][c];
        visit[r][c]=true;
        
        if(cur<=get(grid,r+1,c)){
            dfs(grid,r+1,c,visit);
        }
        
        if(cur<=get(grid,r-1,c)){
            dfs(grid,r-1,c,visit);
        }
        
        if(cur<=get(grid,r,c+1)){
            dfs(grid,r,c+1,visit);
        }
        
        if(cur<=get(grid,r,c-1)){
            dfs(grid,r,c-1,visit);
        }
    }
    
    public int get(int grid[][],int r,int c){
        if(r<0||c<0||r>=grid.length||c>=grid[0].length)return Integer.MIN_VALUE;
        return grid[r][c];
    }
}