Merge pull request neetcode-gh#164 from r1cky0/patch-10

Create 417-Pacific-Atlantic-Water-Flow.java

Author: neetcode-gh

java/417-Pacific-Atlantic-Water-Flow.java

@@ -0,0 +1,39 @@
+class Solution {
+    int[][] dir = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
+    public List<List<Integer>> pacificAtlantic(int[][] heights) {
+        List<List<Integer>> res = new ArrayList<>();
+        
+        int rows = heights.length, cols = heights[0].length;
+        boolean[][] pacific = new boolean[rows][cols];
+        boolean[][] atlantic = new boolean[rows][cols];
+        
+        for (int i = 0; i < cols; i++) {
+            dfs(heights, 0, i, Integer.MIN_VALUE, pacific);
+            dfs(heights, rows - 1, i, Integer.MIN_VALUE, atlantic);
+        }
+        
+        for (int i = 0; i < rows; i++) {
+            dfs(heights, i, 0, Integer.MIN_VALUE, pacific);
+            dfs(heights, i, cols - 1, Integer.MIN_VALUE, atlantic);
+        }
+        
+        for (int i = 0; i < rows; i++) {
+            for (int j = 0; j < cols; j++) {
+                if (pacific[i][j] && atlantic[i][j]) {
+                    res.add(Arrays.asList(i, j));
+                }
+            }
+        }
+        return res;
+    }
+    
+    private void dfs(int[][] heights, int i, int j, int prev, boolean[][] ocean) {
+        if (i < 0 || i >= ocean.length || j < 0 || j >= ocean[0].length) return;
+        if (heights[i][j] < prev || ocean[i][j]) return;
+        
+        ocean[i][j] = true;
+        for (int[] d: dir) {
+            dfs(heights, i + d[0], j + d[1], heights[i][j], ocean);
+        }
+    }
+}