add solution: number-of-islands

Author: dusunax

number-of-islands/dusunax.py

@@ -0,0 +1,38 @@
+'''
+# 200. Number of Islands
+
+use DFS to find the number of islands (to find the all the possible cases)
+
+## Time and Space Complexity
+
+```
+TC: O(m * n)
+SC: O(m * n)
+```
+
+### TC is O(m * n):
+- dfs function is called for each cell in the grid for checking is the land ("1") = O(m * n)
+
+### SC is O(m * n):
+- using a recursive function, the call stack can go as deep as the number of cells in the grid in the worst case. = O(m * n)
+'''
+class Solution:
+    def numIslands(self, grid: List[List[str]]) -> int:
+        def dfs(x, y):
+            if x < 0 or y < 0 or y >= len(grid) or x >= len(grid[0]) or grid[y][x] == "0" :
+                return
+        
+            grid[y][x] = "0"
+            dfs(x, y + 1)
+            dfs(x - 1, y)
+            dfs(x, y - 1)
+            dfs(x + 1, y)
+        
+        island_count = 0
+        for y in range(len(grid)):
+            for x in range(len(grid[0])):
+                if grid[y][x] == "1":
+                    dfs(x, y)
+                    island_count += 1
+
+        return island_count