Merge pull request #2 from sfuSwSo/200-number-of-islands

solution for problem 200

Author: shp2018

Diff for: 200-number-of-islands/solution.py

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+class Solution:
+    def numIslands(self, grid: List[List[str]]) -> int:
+        m = len(grid)
+        n = len(grid[0])
+        count = 0 
+        visited = set()
+        directions=[(-1,0),(0,1),(1,0),(0,-1)]
+
+        def islands(x,y):
+             for dx, dy in directions:
+                nx,ny = x+dx, y+dy
+                if 0<=nx<m and 0<=ny<n and grid[nx][ny]=='1' and (nx,ny) not in visited:
+                    visited.add((nx,ny))
+                    islands(nx,ny)
+
+
+        for x in range(m):
+            for y in range(n):
+                if grid[x][y] == '1' and (x,y) not in visited:
+                    count +=1
+                    visited.add((x,y))
+                    islands(x,y)        
+
+        return count
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