Flowing Water

输入是一个 N*N的矩阵，代表地势高度。如果下雨水流只能流去比他矮或者一样高的地势。

矩阵左边和上边是太平洋，右边和下边是大西洋。求出所有的能同时流到两个大洋的点。

For example:

12345678910

Pacific: ~Atlantic: *~ ~ ~ ~ ~ ~ ~~ 1 2 2 3 (5) *~ 3 2 3 (4) (4) *~ 2 4 (5) 3 1 *~ (6) (7) 1 4 5 *~ (5) 1 1 2 4 ** * * * * * *

括号里即为结果：

[[0,
4], [1, 3], [1, 4], [2, 2], [3, 0], [3, 1], [4, 0]]

import java.util.*;

class Solution {
public List<List<Integer>> waterflow(int[][] map) {
int nrow = map.length;
int ncolumn = map[0].length;
List<List<Integer>> result = new ArrayList<>();
boolean[][] pacificRecord = new boolean[map.length][map[0].length];
boolean[][] atlanticRecord = new boolean [map.length][map[0].length];
for(int i = 0; i < nrow; i++){
DFS(map, i, 0, pacificRecord);
}
for (int i = 0; i < ncolumn; i++){
DFS(map, 0, i, pacificRecord);
}
for(int i = 0; i < nrow; i++){
DFS(map, i, ncolumn - 1, atlanticRecord);
}
for (int i = 0; i < ncolumn; i++){
DFS(map, nrow - 1, i, atlanticRecord);
}

for (int i = 0; i < nrow; i++){
for(int j = 0; j < ncolumn; j++){
if(pacificRecord[i][j] && atlanticRecord[i][j]){
List<Integer> pair = new ArrayList<>();
pair.add(i);
pair.add(j);
result.add(pair);
}
}
}
return result;
}

private void DFS(int[][] map, int row, int column, boolean[][] record) {
if (record[row][column]) {
return;
}
int nrow = map.length;
int ncolumn = map[0].length;
int cur = map[row][column];
record[row][column] = true;
int leftColumn = column - 1;
int rightColumn = column + 1;
int upperRow = row - 1;
int loweRow = row + 1;
if (leftColumn >= 0 && map[row][leftColumn] >= cur)
DFS(map, row, leftColumn, record);
if (rightColumn < ncolumn && map[row][rightColumn] >= cur)
DFS(map, row, rightColumn, record);
if (upperRow >= 0 && map[upperRow][column] >= cur)
DFS(map, upperRow, column, record);
if (loweRow < nrow && map[loweRow][column] >= cur)
DFS(map, loweRow, column, record);
}
}

class Main{
public static void main(String[] args){
int[][] map = new int[][]
{{1,2,2,3,5},
{3,2,3,4,4},
{2,4,5,3,1},
{6,7,1,4,5},
{5,1,1,2,4,}};
Solution sol = new Solution();
List<List<Integer>> result = sol.waterflow(map);
for(List<Integer> pair: result){
System.out.println(pair.get(0) + " " + pair.get(1));
}
return;
}
}