417. 太平洋大西洋水流问题(leetcode)

https://leetcode.cn/problems/pacific-atlantic-water-flow/description/

class Solution {
    List<List<Integer>> res = new ArrayList<>();
    int[] dx={0,1,0,-1};
    int[] dy={1,0,-1,0};
    int n;
    int m;
    int[][] heights;
    boolean[][] vis;
    boolean canWest;
    boolean canEast;
    public List<List<Integer>> pacificAtlantic(int[][] heights) {
        // 思路:dfs搜索每个点是否能到太平和大西
        m=heights.length;
        n=heights[0].length;
        this.heights=heights;
        for(int i=0;i<heights.length;i++)
        {
            for(int j=0;j<heights[i].length;j++)
            {
                vis=new boolean[m][n];
                canWest=false;
                canEast=false;
                dfs(i,j);
                if(canEast && canWest)
                {
                    res.add(List.of(i,j));
                }
            }
        }
        return res;

    }

    void dfs(int x,int y)
    {
        if(x==0 || y==0) canWest=true;
        if(x==m-1 || y==n-1) canEast=true;
        vis[x][y]=true;
        for(int i=0;i<4;i++)
        {
            int a=dx[i]+x,b=dy[i]+y;
            if(a>=0 && b>=0 && a<m && b<n && vis[a][b]==false && heights[x][y]>=heights[a][b])
            {
                dfs(a,b);
            }
        }
    }
}