solve 3

Author: lylaminju

pacific-atlantic-water-flow/pmjuu.py

@@ -0,0 +1,71 @@
+'''
+시간 복잡도: O(m * n)
+- 각 바다에서 BFS를 한 번씩 수행하며, 각 셀을 최대 한 번씩 방문하므로 O(m * n)입니다.
+
+공간 복잡도: O(m * n)
+- BFS 탐색을 위한 큐와 방문한 셀을 저장하는 집합(set)이 필요하므로 O(m * n)입니다.
+'''
+
+from collections import deque
+from typing import List
+
+class Solution:
+    def pacificAtlantic(self, heights: List[List[int]]) -> List[List[int]]:
+        m, n = len(heights), len(heights[0])
+        directions = [(0, 1), (0, -1), (1, 0), (-1, 0)]
+        
+        def bfs(starts):
+            queue = deque(starts)
+            reachable = set(starts)
+            
+            while queue:
+                r, c = queue.popleft()
+                for dr, dc in directions:
+                    nr, nc = r + dr, c + dc
+                    if (0 <= nr < m and 0 <= nc < n and
+                        (nr, nc) not in reachable and
+                        heights[nr][nc] >= heights[r][c]):  # 물이 흐를 수 있는지 확인
+                        queue.append((nr, nc))
+                        reachable.add((nr, nc))
+            
+            return reachable
+
+        # 태평양(왼쪽과 위쪽 가장자리)에서 시작하는 셀들
+        pacific_starts = [(0, c) for c in range(n)] + [(r, 0) for r in range(m)]
+        # 대서양(오른쪽과 아래쪽 가장자리)에서 시작하는 셀들
+        atlantic_starts = [(m-1, c) for c in range(n)] + [(r, n-1) for r in range(m)]
+
+        pacific_reach = bfs(pacific_starts)
+        atlantic_reach = bfs(atlantic_starts)
+
+        return list(pacific_reach & atlantic_reach)
+
+
+class Solution:
+    def pacificAtlantic(self, heights: List[List[int]]) -> List[List[int]]:
+        if not heights or not heights[0]:
+            return []
+        
+        m, n = len(heights), len(heights[0])
+        directions = [(0, 1), (0, -1), (1, 0), (-1, 0)]
+
+        def dfs(r, c, reachable):
+            reachable.add((r, c))
+            for dr, dc in directions:
+                nr, nc = r + dr, c + dc
+                if (0 <= nr < m and 0 <= nc < n and
+                    (nr, nc) not in reachable and
+                    heights[nr][nc] >= heights[r][c]):
+                    dfs(nr, nc, reachable)
+
+        pacific_reach, atlantic_reach = set(), set()
+
+        for c in range(n):
+            dfs(0, c, pacific_reach)
+            dfs(m-1, c, atlantic_reach)
+
+        for r in range(m):
+            dfs(r, 0, pacific_reach)
+            dfs(r, n-1, atlantic_reach)
+
+        return list(pacific_reach & atlantic_reach)