题目：

题解：

class Solution {static int[][] dirs = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};int[][] heights;int m, n;public List<List<Integer>> pacificAtlantic(int[][] heights) {this.heights = heights;this.m = heights.length;this.n = heights[0].length;boolean[][] pacific = new boolean[m][n];boolean[][] atlantic = new boolean[m][n];for (int i = 0; i < m; i++) {bfs(i, 0, pacific);}for (int j = 1; j < n; j++) {bfs(0, j, pacific);}for (int i = 0; i < m; i++) {bfs(i, n - 1, atlantic);}for (int j = 0; j < n - 1; j++) {bfs(m - 1, j, atlantic);}List<List<Integer>> result = new ArrayList<List<Integer>>();for (int i = 0; i < m; i++) {for (int j = 0; j < n; j++) {if (pacific[i][j] && atlantic[i][j]) {List<Integer> cell = new ArrayList<Integer>();cell.add(i);cell.add(j);result.add(cell);}}}return result;}public void bfs(int row, int col, boolean[][] ocean) {if (ocean[row][col]) {return;}ocean[row][col] = true;Queue<int[]> queue = new ArrayDeque<int[]>();queue.offer(new int[]{row, col});while (!queue.isEmpty()) {int[] cell = queue.poll();for (int[] dir : dirs) {int newRow = cell[0] + dir[0], newCol = cell[1] + dir[1];if (newRow >= 0 && newRow < m && newCol >= 0 && newCol < n && heights[newRow][newCol] >= heights[cell[0]][cell[1]] && !ocean[newRow][newCol]) {ocean[newRow][newCol] = true;queue.offer(new int[]{newRow, newCol});}}}}
}