floodfill算法系列一＞太平洋大西洋水流问题

题目方法解析：

代码设计：

代码呈现：

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);}}}
}