Merge pull request #2669 from sunlight0602/0104-make-largest-island

104.建造最大岛屿 python DFS solution

problems/kamacoder/0104.建造最大岛屿.md

@@ -366,6 +366,79 @@ public class Main {
 
 ### Python
 
+```Python
+import collections
+
+directions = [[-1, 0], [0, 1], [0, -1], [1, 0]]
+area = 0
+
+def dfs(i, j, grid, visited, num):
+    global area
+    
+    if visited[i][j]:
+        return
+
+    visited[i][j] = True
+    grid[i][j] = num  # 标记岛屿号码
+    area += 1
+    
+    for x, y in directions:
+        new_x = i + x
+        new_y = j + y
+        if (
+            0 <= new_x < len(grid)
+            and 0 <= new_y < len(grid[0])
+            and grid[new_x][new_y] == "1"
+        ):
+            dfs(new_x, new_y, grid, visited, num)
+    
+
+def main():
+    global area
+    
+    N, M = map(int, input().strip().split())
+    grid = []
+    for i in range(N):
+        grid.append(input().strip().split())
+    visited = [[False] * M for _ in range(N)]
+    rec = collections.defaultdict(int)
+    
+    cnt = 2
+    for i in range(N):
+        for j in range(M):
+            if grid[i][j] == "1":
+                area = 0
+                dfs(i, j, grid, visited, cnt)
+                rec[cnt] = area  # 纪录岛屿面积
+                cnt += 1
+    
+    res = 0
+    for i in range(N):
+        for j in range(M):
+            if grid[i][j] == "0":
+                max_island = 1  # 将水变为陆地，故从1开始计数
+                v = set()
+                for x, y in directions:
+                    new_x = i + x
+                    new_y = j + y
+                    if (
+                        0 <= new_x < len(grid)
+                        and 0 <= new_y < len(grid[0])
+                        and grid[new_x][new_y] != "0"
+                        and grid[new_x][new_y] not in v  # 岛屿不可重复
+                    ):
+                        max_island += rec[grid[new_x][new_y]]
+                        v.add(grid[new_x][new_y])
+                res = max(res, max_island)
+
+    if res == 0:
+        return max(rec.values())  # 无水的情况
+    return res
+    
+if __name__ == "__main__":
+    print(main())
+```
+
 ### Go
 
 ### Rust