130

130 Surrounded Regions.py

@@ -0,0 +1,91 @@
+"""
+Given a 2D board containing 'X' and '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
+"""
+__author__ = 'Danyang'
+CONNECTED = 'C'
+class Solution:
+    def solve(self, board):
+        """
+        Graph Theory
+        Algorithm1: bfs, to tell whether it is on the boarder
+        Algorithm2: bfs, to get the connectivity graph
+        :param board: a 2D array
+        :return: NIL, Capture all regions by modifying the input board in-place.
+        """
+        if not board or not board[0]:
+            return
+        q = []
+        # scan the boarder
+        m = len(board)
+        n = len(board[0])
+        for i in xrange(m):
+            if board[i][0]=='O': q.append((i, 0))
+            if board[i][n-1]=='O': q.append((i, n-1))
+        for j in xrange(1, n-1):
+            if board[0][j]=='O': q.append((0, j))
+            if board[m-1][j]=='O': q.append((m-1, j))
+
+        i = 0
+        while i<len(q): # dynamically expanding, no deletion of elements
+            cor = q[i]
+            board[cor[0]][cor[1]]=CONNECTED
+            try: # left
+                if board[cor[0]][cor[1]-1]=='O': q.append((cor[0], cor[1]-1))
+            except IndexError:
+                pass
+            try: # right
+                if board[cor[0]][cor[1]+1]=='O': q.append((cor[0], cor[1]+1))
+            except IndexError:
+                pass
+            try: # up
+                if board[cor[0]-1][cor[1]]=='O': q.append((cor[0]-1, cor[1]))
+            except IndexError:
+                pass
+            try: # down
+                if board[cor[0]+1][cor[1]]=='O': q.append((cor[0]+1, cor[1]))
+            except IndexError:
+                pass
+
+            i += 1
+
+        for i in xrange(m):
+            for j in xrange(n):
+                if board[i][j]=='O':
+                    board[i][j] = 'X'
+                elif board[i][j]==CONNECTED:
+                    board[i][j] = 'O'
+
+
+if __name__=="__main__":
+    board = [
+        ['X', 'X', 'X', 'X'],
+        ['X', 'O', 'O', 'X'],
+        ['X', 'X', 'O', 'X'],
+        ['X', 'O', 'X', 'X']
+    ]
+    expected_board = [
+        ['X', 'X', 'X', 'X'],
+        ['X', 'X', 'X', 'X'],
+        ['X', 'X', 'X', 'X'],
+        ['X', 'O', 'X', 'X']
+    ]
+    Solution().solve(board)
+    assert board==expected_board
+
+
+
+

README.md

@@ -20,8 +20,8 @@ Welcome to raise an issue [here](https://github.com/zhangdanyangg/LeetCode/issue
 ### Notes
 Failed attempts are kept in the source code, which are annotated as TLE (Time Limit Exceeds) or MLE (Memory Limit Exceeds).
 
-### TODO
-Question burn-down rate: 151/152 completed
+### Completion
+Questions: 152/152 completed
 
 ###Miscellaneous
 Practice