add pacific atlantic water flow solution

Author: Tessa1217

pacific-atlantic-water-flow/Tessa1217.java

@@ -0,0 +1,140 @@
+import java.util.ArrayList;
+import java.util.List;
+
+class Solution {
+
+    int[] dx = {1, -1, 0, 0};
+    int[] dy = {0, 0, 1, -1};
+    // boolean[][] visited;
+    int width, height;
+
+    // 시간복잡도, 공간복잡도: O(m * n)
+    public List<List<Integer>> pacificAtlantic(int[][] heights) {
+        height = heights.length;
+        width = heights[0].length;
+
+        boolean[][] pacific = new boolean[height][width];
+        boolean[][] atlantic = new boolean[height][width];
+
+        /**
+         * 가장자리에 도달하는 경로를 일일이 탐색하는 것이 아닌 
+         가장자리부터 물이 흐를 수 있는 경로를 역으로 탐색
+         */
+
+        // height check
+        for (int i = 0; i < height; i++) {
+            dfs(i, 0, heights, pacific);
+            dfs(i, width - 1, heights, atlantic);
+        }
+
+        // width check
+        for (int j = 0; j < width; j++) {
+            dfs(0, j, heights, pacific);
+            dfs(height - 1, j, heights, atlantic);
+        }
+
+        List<List<Integer>> answer = new ArrayList<>();
+        for (int i = 0; i < height; i++) {
+            for (int j = 0; j < width; j++) {
+                if (pacific[i][j] && atlantic[i][j]) {
+                    answer.add(List.of(i, j));
+                }
+            }
+        }
+
+        return answer;
+    }
+
+    private void dfs(int x, int y, int[][] heights, boolean[][] visited) {
+        visited[x][y] = true;
+        for (int i = 0; i < 4; i++) {
+            int nx = x + dx[i];
+            int ny = y + dy[i];
+            if (nx >= 0 && nx < height && ny >= 0 && ny < width) {
+                if (!visited[nx][ny] && heights[nx][ny] >= heights[x][y]) {
+                    dfs(nx, ny, heights, visited);
+                }
+            }
+        }
+    }
+
+    // public List<List<Integer>> pacificAtlantic(int[][] heights) {
+    //     height = heights.length;
+    //     width = heights[0].length;
+    //     visited = new boolean[height][width];
+
+    //     List<List<Integer>> answer = new ArrayList<>();
+    //     for (int i = 0; i < height; i++) {
+    //         for (int j = 0; j < width; j++) {                
+    //             WaterFlow checkWaterFlow = dfs(i, j, new WaterFlow(), heights);
+    //             if (checkWaterFlow.crossBothOceans()) {
+    //                 List<Integer> coordinate = List.of(i, j);                    
+    //                 answer.add(coordinate);
+    //             }
+    //         }
+    //     }
+    //     return answer;
+    // }
+
+    // private WaterFlow dfs(int x, int y, WaterFlow checkWaterFlow, int[][] heights) {
+    //     /**
+    //     0, 0 | 0, 1 | 0, 2 | 0, 3 | 0, 4 
+    //     1, 0 | 2, 0 | 3, 0 | 4, 0
+    //         */
+    //     if (x == 0 || y == 0) {
+    //         checkWaterFlow.crossPacificFlow();
+    //     }
+    //     /**
+    //     4, 0 | 4, 1 | 4, 2 | 4, 3 | 4, 4
+    //     3, 4 | 2, 4 | 1, 4 | 0, 4
+    //         */
+    //     if (x == height - 1 || y == width - 1) {
+    //         checkWaterFlow.crossAtlanticFlow();
+    //     }
+
+    //     if (checkWaterFlow.crossBothOceans()) {
+    //         return checkWaterFlow;
+    //     }
+
+    //     visited[x][y] = true;
+
+    //     for (int i = 0; i < 4; i++) {
+    //         int nx = x + dx[i];
+    //         int ny = y + dy[i];
+    //         if (nx >= 0 && nx < height && ny >= 0 && ny < width) {
+    //             if (!visited[nx][ny] && heights[nx][ny] <= heights[x][y]) {
+    //                 dfs(nx, ny, checkWaterFlow, heights);            
+    //             }                
+    //         }            
+    //     }
+    //     visited[x][y] = false;
+
+    //     return checkWaterFlow;
+    // }
+
+    // static class WaterFlow {
+
+    //     private boolean pacificFlow;
+
+    //     private boolean atlanticFlow;
+
+    //     WaterFlow() {
+    //         pacificFlow = false;
+    //         atlanticFlow = false;
+    //     }
+
+    //     public void crossPacificFlow() {
+    //         pacificFlow = true;
+    //     }
+
+    //     public void crossAtlanticFlow() {
+    //         atlanticFlow = true;
+    //     }
+
+    //     public boolean crossBothOceans() {
+    //         return pacificFlow && atlanticFlow;
+    //     }
+
+    // }
+}
+