区域包围问题(类似于岛屿问题, dfs)

Author: cls1991

DepthFirstSearch/129_SumRootToLeafNumbers.py

@@ -38,20 +38,14 @@ def sumNumbers(self, root):
         :type root: TreeNode
         :rtype: int
         """
+        return self.dfs(root, 0)
+
+    def dfs(self, root, sub):
         if not root:
             return 0
 
-        sub = 0
-        total = []
-        self.dfs(root, sub, total)
-
-        return sum(total)
-
-    def dfs(self, root, sub, total):
         sub = 10 * sub + root.val
         if not root.left and not root.right:
-            total.append(sub)
-        if root.left:
-            self.dfs(root.left, sub, total)
-        if root.right:
-            self.dfs(root.right, sub, total)
+            return sub
+
+        return self.dfs(root.left, sub) + self.dfs(root.right, sub)

DepthFirstSearch/130_SurroundedRegions.py

@@ -0,0 +1,57 @@
+# coding: utf8
+
+
+"""
+    题目链接: https://leetcode.com/problems/surrounded-regions/description.
+    题目描述:
+
+    Given a 2D board containing 'X' and 'O' (the letter O), capture all regions surrounded by 'X'.
+
+    A region is captured by flipping all 'O's into 'X's in that surrounded region.
+
+    For example,
+        X X X X
+        X O O X
+        X X O X
+        X O X X
+        After running your function, the board should be:
+
+        X X X X
+        X X X X
+        X X X X
+        X O X X
+
+"""
+
+
+class Solution(object):
+    def solve(self, board):
+        """
+        :type board: List[List[str]]
+        :rtype: void Do not return anything, modify board in-place instead.
+        """
+        if not any(board):
+            return
+
+        rows, columns = len(board), len(board[0])
+        for i in range(rows):
+            for j in range(columns):
+                if i == 0 or i == rows - 1 or j == 0 or j == columns - 1 and board[i][j] == 'O':
+                    self.dfs(board, rows, columns, i, j)
+
+        for i in range(rows):
+            for j in range(columns):
+                if board[i][j] == 'O':
+                    board[i][j] = 'X'
+                elif board[i][j] == '$':
+                    board[i][j] = 'O'
+
+    def dfs(self, board, rows, columns, i, j):
+        if i < 0 or i >= rows or j < 0 or j >= columns or board[i][j] != 'O':
+            return
+
+        board[i][j] = '$'
+        self.dfs(board, rows, columns, i - 1, j)
+        self.dfs(board, rows, columns, i, j + 1)
+        self.dfs(board, rows, columns, i + 1, j)
+        self.dfs(board, rows, columns, i, j - 1)