pacific atlantic water flow

Author: se6816

pacific-atlantic-water-flow/se6816.java

@@ -0,0 +1,73 @@
+/**
+    BFS를 통해, 방문 지점이 겹치는 부분을 찾는 방식
+ */
+class Solution {
+    public static int[] moveX = {0, 1, 0, -1};
+    public static int[] moveY = {1, 0, -1, 0};
+    public boolean[][] POvisited;
+    public boolean[][] AOvisited;
+    public int N;
+    public int M;
+    public List<List<Integer>> pacificAtlantic(int[][] heights) {
+        List<List<Integer>> result = new ArrayList<>();
+        N = heights.length;
+        M = heights[0].length;
+        POvisited = new boolean[N][M];
+        AOvisited = new boolean[N][M];
+        Queue<int[]> que = new LinkedList<>();
+        Queue<int[]> que2 = new LinkedList<>();
+
+        for(int i = 0; i < M; i++) {
+            POvisited[0][i] = true;
+            que.add(new int[]{0, i});
+            AOvisited[N-1][i] = true;
+            que2.add(new int[]{N-1, i});
+        }
+
+        for(int i = 0; i < N; i++) {
+            POvisited[i][0] = true;
+            que.add(new int[]{i, 0});
+            AOvisited[i][M-1] = true;
+            que2.add(new int[]{i, M-1});
+        }
+        bfs(que, POvisited, heights);
+        bfs(que2, AOvisited, heights);
+
+        for(int i = 0; i < N; i++) {
+            for(int j = 0; j < M; j++) {
+                if(POvisited[i][j] && AOvisited[i][j]) {
+                    result.add(new ArrayList<>(List.of(i, j)));
+                }
+            }
+        }
+
+        return result;
+    }
+
+    public void bfs(Queue<int[]> que, boolean[][] visited, int[][] heights) {
+        while(!que.isEmpty()) {
+            int[] node = que.poll();
+            for(int i = 0; i < 4; i++) {
+                int tempX = node[0] + moveX[i];
+                int tempY = node[1] + moveY[i];
+                if(isOutOfIndex(tempX, tempY)) {
+                    continue;
+                }
+
+                if(visited[tempX][tempY]) {
+                    continue;
+                }
+                if(heights[tempX][tempY] < heights[node[0]][node[1]]) {
+                    continue;
+                }
+
+                visited[tempX][tempY] = true;
+                que.add(new int[]{tempX, tempY});
+            }
+        }
+    }
+
+    public boolean isOutOfIndex(int x, int y){
+        return x < 0 || x >= N || y < 0 || y >= M;
+    }
+}