[LeetCode] Surrounded Regions 包围区域

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

参考资料：

[LeetCode] Surrounded Regions 包围区域

原文：http://www.cnblogs.com/grandyang/p/4555831.html