solve pacific altantic water flow

Author: sora0319

pacific-atlantic-water-flow/sora0319.java

@@ -0,0 +1,67 @@
+public class sora0319 {
+    public class Solution {
+        private int[][] heights;
+        private int rows, cols;
+
+        public List<List<Integer>> pacificAtlantic(int[][] heights) {
+            this.heights = heights;
+            this.rows = heights.length;
+            this.cols = heights[0].length;
+            List<List<Integer>> result = new ArrayList<>();
+
+            for (int row = 0; row < rows; row++) {
+                for (int col = 0; col < cols; col++) {
+                    Set<String> visitedPac = new HashSet<>();
+                    Set<String> visitedAtl = new HashSet<>();
+
+                    if (dfsPac(row, col, visitedPac) && dfsAtl(row, col, visitedAtl)) {
+                        result.add(Arrays.asList(row, col));
+                    }
+                }
+            }
+            return result;
+        }
+
+        private boolean dfsPac(int row, int col, Set<String> visited) {
+            String key = row + "," + col;
+            if (visited.contains(key)) return false;
+            visited.add(key);
+
+            if (row == 0 || col == 0) return true;
+
+            int[][] moved = { {0, -1}, {0, 1}, {-1, 0}, {1, 0} };
+            for (int[] m : moved) {
+                int r = row + m[0];
+                int c = col + m[1];
+                if (isRange(r, c) && heights[row][col] >= heights[r][c]) {
+                    if (dfsPac(r, c, visited)) return true;
+                }
+            }
+            return false;
+        }
+
+        private boolean dfsAtl(int row, int col, Set<String> visited) {
+            String key = row + "," + col;
+            if (visited.contains(key)) return false;
+            visited.add(key);
+
+            if (row == rows - 1 || col == cols - 1) return true;
+
+            int[][] directions = { {0, -1}, {0, 1}, {-1, 0}, {1, 0} };
+            for (int[] dir : directions) {
+                int r = row + dir[0];
+                int c = col + dir[1];
+                if (isRange(r, c) && heights[row][col] >= heights[r][c]) {
+                    if (dfsAtl(r, c, visited)) return true;
+                }
+            }
+            return false;
+        }
+
+        private boolean isRange(int r, int c) {
+            return r >= 0 && r < rows && c >= 0 && c < cols;
+        }
+    }
+
+}
+