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Solution.java
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Solution.java
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package g0401_0500.s0417_pacific_atlantic_water_flow;
// #Medium #Array #Depth_First_Search #Breadth_First_Search #Matrix
// #Graph_Theory_I_Day_4_Matrix_Related_Problems #Level_2_Day_10_Graph/BFS/DFS #Udemy_Graph
// #2022_07_16_Time_5_ms_(92.62%)_Space_54.8_MB_(59.96%)
import java.util.ArrayList;
import java.util.List;
public class Solution {
private int col = 0;
private int row = 0;
public List<List<Integer>> pacificAtlantic(int[][] matrix) {
List<List<Integer>> res = new ArrayList<>();
if (matrix.length == 0) {
return res;
}
col = matrix.length;
row = matrix[0].length;
boolean[][] pacific = new boolean[col][row];
boolean[][] atlantic = new boolean[col][row];
for (int i = 0; i < col; i++) {
dfs(i, 0, matrix, pacific);
dfs(i, row - 1, matrix, atlantic);
}
for (int i = 0; i < row; i++) {
dfs(0, i, matrix, pacific);
dfs(col - 1, i, matrix, atlantic);
}
for (int i = 0; i < col; i++) {
for (int j = 0; j < row; j++) {
if (pacific[i][j] && atlantic[i][j]) {
List<Integer> temp = new ArrayList<>();
temp.add(i);
temp.add(j);
res.add(temp);
}
}
}
return res;
}
private void dfs(int i, int j, int[][] matrix, boolean[][] visited) {
if (i < 0 || j < 0 || i >= matrix.length || j >= matrix[0].length || visited[i][j]) {
return;
}
visited[i][j] = true;
if (i < col - 1 && matrix[i][j] <= matrix[i + 1][j]) {
dfs(i + 1, j, matrix, visited);
}
if (i > 0 && matrix[i][j] <= matrix[i - 1][j]) {
dfs(i - 1, j, matrix, visited);
}
if (j < row - 1 && matrix[i][j] <= matrix[i][j + 1]) {
dfs(i, j + 1, matrix, visited);
}
if (j > 0 && matrix[i][j] <= matrix[i][j - 1]) {
dfs(i, j - 1, matrix, visited);
}
}
}