- Pacific Atlantic Water Flow #260

Author: ayosecu

pacific-atlantic-water-flow/ayosecu.py

@@ -0,0 +1,66 @@
+from typing import List
+from collections import deque
+
+class Solution:
+    """
+        - Time Complexity: O(mn)
+        - Space Complexity: O(mn)
+    """
+    def pacificAtlantic(self, heights: List[List[int]]) -> List[List[int]]:
+        m, n = len(heights), len(heights[0])
+
+        # Visit checking for each ocean
+        p_visited = [[False] * n for _ in range(m)]
+        a_visited = [[False] * n for _ in range(m)]
+
+        def bfs(q, visited):
+            dir = [(-1, 0), (0, -1), (1, 0), (0, 1)]
+            while q:
+                r, c = q.popleft()
+                for dx, dy in dir:
+                    next_r, next_c = r + dx, c + dy
+                    # checking next cell is not visited and higher than current cell
+                    if ( 0 <= next_r < m and 0 <= next_c < n and not visited[next_r][next_c]
+                        and heights[next_r][next_c] >= heights[r][c] ):
+                        visited[next_r][next_c] = True
+                        q.append((next_r, next_c))
+                    
+        p_dq, a_dq = deque(), deque()
+
+        for i in range(m):
+            # left side (pacific)
+            p_dq.append((i, 0))
+            p_visited[i][0] = True
+            # right side (atlantic)
+            a_dq.append((i, n - 1))
+            a_visited[i][n - 1] = True
+        
+        for j in range(n):
+            # top side (pacific)
+            p_dq.append((0, j))
+            p_visited[0][j] = True
+            # bottom side (atlantic)
+            a_dq.append((m - 1, j))
+            a_visited[m - 1][j] = True
+        
+        bfs(p_dq, p_visited)
+        bfs(a_dq, a_visited)
+
+        result = []
+        for i in range(m):
+            for j in range(n):
+                if p_visited[i][j] and a_visited[i][j]:
+                    # both of oceans are accessible
+                    result.append([i, j])
+        
+        return result
+
+tc = [
+        ([[1,2,2,3,5],[3,2,3,4,4],[2,4,5,3,1],[6,7,1,4,5],[5,1,1,2,4]], [[0,4],[1,3],[1,4],[2,2],[3,0],[3,1],[4,0]]),
+        ([[1]], [[0,0]])
+]
+
+sol = Solution()
+for i, (h, e) in enumerate(tc, 1):
+    r = sol.pacificAtlantic(h)
+    print(f"TC {i} is Passed!" if r == e else f"TC {i} is Failed! - Expected: {e}, Result: {r}")