2022-08-31 update: added "Pacific Atlantic Water Flow" (#78)

Author: fartem

src/main/java/com/smlnskgmail/jaman/leetcodejava/medium/PacificAtlanticWaterFlow.java

@@ -0,0 +1,59 @@
+package com.smlnskgmail.jaman.leetcodejava.medium;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+// https://leetcode.com/problems/pacific-atlantic-water-flow/
+public class PacificAtlanticWaterFlow {
+
+    private final int[][] input;
+
+    public PacificAtlanticWaterFlow(int[][] input) {
+        this.input = input;
+    }
+
+    public List<List<Integer>> solution() {
+        int r = input.length;
+        int c = input[0].length;
+        boolean[][] atlantic = new boolean[r][c];
+        boolean[][] pacific = new boolean[r][c];
+        for (int i = 0; i < r; i++) {
+            for (int j = 0; j < c; j++) {
+                if (i == 0 || j == 0) {
+                    dfs(pacific, input, i, j, 0);
+                }
+                if (i == r - 1 || j == c - 1) {
+                    dfs(atlantic, input, i, j, 0);
+                }
+            }
+        }
+        List<List<Integer>> result = new ArrayList<>();
+        for (int i = 0; i < r; i++) {
+            for (int j = 0; j < c; j++) {
+                if (atlantic[i][j] && pacific[i][j]) {
+                    result.add(Arrays.asList(i, j));
+                }
+            }
+        }
+        return result;
+    }
+
+    private void dfs(boolean[][] sea, int[][] grid, int r, int c, int prev) {
+        if (r < 0 || r >= grid.length || c < 0 || c >= grid[0].length) {
+            return;
+        }
+        if (grid[r][c] < prev) {
+            return;
+        }
+        if (sea[r][c]) {
+            return;
+        }
+        sea[r][c] = true;
+        dfs(sea, grid, r + 1, c, grid[r][c]);
+        dfs(sea, grid, r - 1, c, grid[r][c]);
+        dfs(sea, grid, r, c + 1, grid[r][c]);
+        dfs(sea, grid, r, c - 1, grid[r][c]);
+    }
+
+}

src/test/java/com/smlnskgmail/jaman/leetcodejava/medium/PacificAtlanticWaterFlowTest.java

@@ -0,0 +1,35 @@
+package com.smlnskgmail.jaman.leetcodejava.medium;
+
+import org.junit.Test;
+
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class PacificAtlanticWaterFlowTest {
+
+    @Test
+    public void defaultTest() {
+        assertEquals(
+                List.of(
+                        List.of(0, 4),
+                        List.of(1, 3),
+                        List.of(1, 4),
+                        List.of(2, 2),
+                        List.of(3, 0),
+                        List.of(3, 1),
+                        List.of(4, 0)
+                ),
+                new PacificAtlanticWaterFlow(
+                        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()
+        );
+    }
+
+}