solve(w07): 200. Number of Islands

Author: seungriyou

number-of-islands/seungriyou.py

@@ -0,0 +1,76 @@
+# https://leetcode.com/problems/number-of-islands/
+
+from typing import List
+
+class Solution:
+    def numIslands_bfs(self, grid: List[List[str]]) -> int:
+        """
+        [Complexity]
+            - TC: O(m * n)
+            - SC: O(m * n)
+
+        [Approach]
+            BFS를 사용한다.
+        """
+        from collections import deque
+
+        dr, dc = [-1, 1, 0, 0], [0, 0, -1, 1]
+        m, n = len(grid), len(grid[0])
+        res = 0
+
+        def bfs(r, c):
+            q = deque([(r, c)])
+            grid[r][c] = "0"
+
+            while q:
+                r, c = q.popleft()
+
+                for i in range(4):
+                    nr, nc = r + dr[i], c + dc[i]
+                    # nr, nc가 (1) 범위 내이면서 (2) 아직 방문하지 않은 곳이라면
+                    if 0 <= nr < m and 0 <= nc < n and grid[nr][nc] == "1":
+                        q.append((nr, nc))
+                        grid[nr][nc] = "0"
+
+        for r in range(m):
+            for c in range(n):
+                if grid[r][c] == "1":
+                    bfs(r, c)
+                    res += 1
+
+        return res
+
+    def numIslands(self, grid: List[List[str]]) -> int:
+        """
+        [Complexity]
+            - TC: O(m * n)
+            - SC: O(m * n) (call stack)
+
+        [Approach]
+            DFS를 사용한다.
+        """
+        dr, dc = [-1, 1, 0, 0], [0, 0, -1, 1]
+        m, n = len(grid), len(grid[0])
+        res = 0
+
+        def dfs(r, c):
+            # base condition
+            if not (0 <= r < m and 0 <= c < n) or grid[r][c] == "0":
+                return
+
+            # visited 처리
+            grid[r][c] = "0"
+
+            # recur
+            dfs(r - 1, c)
+            dfs(r + 1, c)
+            dfs(r, c - 1)
+            dfs(r, c + 1)
+
+        for r in range(m):
+            for c in range(n):
+                if grid[r][c] == "1":
+                    dfs(r, c)
+                    res += 1
+
+        return res