solve : pacific-atlantic water flow

Author: SamTheKorean

pacific-atlantic-water-flow/samthekorean.py

@@ -0,0 +1,44 @@
+# m is number of rows and n is number of columns
+# TC : O(m*n)
+# SC : O(m*n)
+class Solution:
+    def pacificAtlantic(self, heights: List[List[int]]) -> List[List[int]]:
+        ROWS, COLS = len(heights), len(heights[0])
+        DIRECTIONS = [(1, 0), (-1, 0), (0, 1), (0, -1)]
+        pacific, atlantic = set(), set()
+        result: List[List[int]] = []
+
+        def dfs(
+            r: int, c: int, ocean_set: Set[Tuple[int, int]], prev_height: int
+        ) -> None:
+            if (
+                r < 0
+                or r >= ROWS
+                or c < 0
+                or c >= COLS
+                or (r, c) in ocean_set
+                or heights[r][c] < prev_height
+            ):
+                return
+
+            ocean_set.add((r, c))
+
+            for dr, dc in DIRECTIONS:
+                dfs(r + dr, c + dc, ocean_set, heights[r][c])
+
+        # Water Flow Simulation from Pacific (Top and Left borders)
+        for col in range(COLS):
+            dfs(0, col, pacific, heights[0][col])
+            dfs(ROWS - 1, col, atlantic, heights[ROWS - 1][col])
+
+        for row in range(ROWS):
+            dfs(row, 0, pacific, heights[row][0])
+            dfs(row, COLS - 1, atlantic, heights[row][COLS - 1])
+
+        # Finding cells reachable by both Pacific and Atlantic
+        for r in range(ROWS):
+            for c in range(COLS):
+                if (r, c) in pacific and (r, c) in atlantic:
+                    result.append([r, c])
+
+        return result