number of islands solution

Author: jungsiroo

number-of-islands/jungsiroo.py

@@ -0,0 +1,50 @@
+class Solution:
+    def numIslands(self, grid: List[List[str]]) -> int:
+		# TC : O(n*m)
+		# SC : O(n*m)
+
+        m, n = len(grid), len(grid[0])
+        dx = [-1,1,0,0]
+        dy = [0,0,-1,1]
+
+        def in_range(r, c):
+            if r<0 or c<0 or r>=m or c>=n:
+                return False
+            return True
+
+        # DFS Way
+
+        def dfs(r, c):
+            grid[r][c] = 'x'
+
+            for i in range(4):
+                nr, nc = r+dx[i], c+dy[i]
+                if not in_range(nr, nc) or grid[nr][nc] != '1':
+                    continue
+                dfs(nr, nc)
+        
+        # BFS Way
+        from collections import deque
+        def bfs(r, c):
+            grid[r][c] = 'x'
+            queue = deque()
+            queue.append([r, c])
+
+            while queue:
+                cr, cc = queue.popleft()
+                for i in range(4):
+                    nr, nc = cr+dx[i], cc+dy[i]
+                    
+                    if not in_range(nr, nc) or grid[nr][nc] != '1':
+                        continue
+                    grid[nr][nc] = 'x'
+                    queue.append([nr, nc])
+
+        ret = 0
+        for i in range(m):
+            for j in range(n):
+                if grid[i][j] == '1':
+                    bfs(i, j)
+                    ret += 1
+        return ret
+