[LeetCode] Surrounded Regions

문제

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.

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

Explanation:

Surrounded regions shouldn’t be on the border, which means that any 'O' on the border of the board are not flipped to 'X'. Any 'O' that is not on the border and it is not connected to an 'O' on the border will be flipped to 'X'. Two cells are connected if they are adjacent cells connected horizontally or vertically.

 

Approach

BFS로 푼다. 벡터에 X로 바꿀 O의 좌표를 저장하되, 가장자리가 뚫려있으면 바꾸지 않는다.

 

Code

https://github.com/chi3236/algorithm/blob/master/LeetCode_SurroundedRegions.cpp