floodfill算法系列一＞太平洋大西洋水流问题

class Solution {
    int m,n;
    int[] dx = {0,0,-1,1};
    int[] dy = {-1,1,0,0};

    public List<List<Integer>> pacificAtlantic(int[][] heights) {
        m = heights.length; n = heights[0].length;
        boolean[][] pac = new boolean[m][n];
        boolean[][] atl = new boolean[m][n];

        //判断大西洋的水能否流到某一位置
        for(int i = 0; i < n; i++) dfs(heights,0,i,pac);
        for(int j = 0; j < m; j++) dfs(heights,j,0,pac);

        //判断太平洋的水能否流到某一位置
        for(int i = 0; i < m; i++) dfs(heights,i,n-1,atl);
        for(int j = 0; j < n; j++) dfs(heights,m-1,j,atl);

        List<List<Integer>> ret = new ArrayList<>();
        for(int i = 0; i < m; i++)
            for(int j = 0; j < n; j++){
                if(pac[i][j] && atl[i][j]){
                    List<Integer> tmp = new ArrayList<>();
                    tmp.add(i); tmp.add(j);
                    ret.add(tmp);
                }
            }

        return ret;
    }

    //封装出来一套标记遍历
    private void dfs(int[][] heights, int i, int j, boolean[][] vis){

        vis[i][j] = true;
        for(int k = 0; k < 4; k++){
            int x = i + dx[k]; int y = j + dy[k];
            if(x >= 0 && x < m && y >= 0 && y < n && !vis[x][y] && heights[x][y] >= heights[i][j]){
                dfs(heights,x,y,vis);
            }
        }
    }
}