feat: [Week 09-3] solve pacific atlantic water flow

Author: Chaedie

pacific-atlantic-water-flow/Chaedie.py

@@ -0,0 +1,33 @@
+"""
+Solution: 
+    1) 가장자리에서 시작해서 어디까지 올라갈수있는지 체크한다.
+    2) 교집합을 찾는다.
+
+Time: O(m * n)
+Space: O(m * n)
+"""
+
+
+class Solution:
+    def pacificAtlantic(self, heights: List[List[int]]) -> List[List[int]]:
+        ROWS, COLS = len(heights), len(heights[0])
+        pacific, atlantic = set(), set()
+
+        def dfs(visit, r, c):
+            if (r, c) in visit:
+                return
+            visit.add((r, c))
+
+            for i, j in [(r + 1, c), (r - 1, c), (r, c + 1), (r, c - 1)]:
+                if 0 <= i and i < ROWS and 0 <= j and j < COLS:
+                    if heights[i][j] >= heights[r][c]:
+                        dfs(visit, i, j)
+
+        for i in range(ROWS):
+            dfs(pacific, i, 0)
+            dfs(atlantic, i, COLS - 1)
+        for i in range(COLS):
+            dfs(pacific, 0, i)
+            dfs(atlantic, ROWS - 1, i)
+
+        return list(pacific.intersection(atlantic))