代码改变世界

Surrounded Regions

2015-04-10 19:55  笨笨的老兔子  阅读(131)  评论(0)  编辑  收藏  举报

给定一个由字符'X'和‘O’组成的矩阵，消除所有被‘X’包围的‘O’

X X X X
X O O X
X X O X
X O X X
变成
X X X X
X X X X
X X X X
X O X X
思路：有点像围棋里一块区域是否有气，只有有气的才能存活下来。即只有‘O’到达了四条边界才可以存活，因此从四条边界开始做广搜，将所有搜索到的'O'赋值为‘1’，然后遍历整个矩阵将所有之前没有被赋值的‘O’赋值为‘X’，将‘1’还原为‘O’即可。

  1. class Solution {
  2. public:
  3.     void solve(vector<vector<char>> &board) {
  4.         if (board.empty())
  5.             return;
  6.         int width = board[0].size();
  7.         int height = board.size();
  8.         for (size_t i = 0; i < width; i++)
  9.         {
  10.             if (board[0][i] == 'O')
  11.                 bfs(0, i, board);
  12.             if (board[height - 1][i] == 'O')
  13.                 bfs(height-1, i, board);
  14.         }
  15.         for (size_t i = 0; i < height; i++)
  16.         {
  17.             if (board[i][0] == 'O')
  18.                 bfs(i, 0, board);
  19.             if (board[i][width - 1] == 'O')
  20.                 bfs(i, width - 1, board);
  21.         }
  22.         for (size_t i = 0; i < height; i++)
  23.         {
  24.             for (size_t j = 0; j < width; j++)
  25.             {
  26.                 if (board[i][j] == '1')
  27.                     board[i][j] = 'O';
  28.                 else if (board[i][j] == 'O')
  29.                 {
  30.                     board[i][j] = 'X';
  31.                 }
  32.             }
  33.         }
  35.     }
  36.     void bfs(int x,int y, vector<vector<char> >&board)
  37.     {
  38.         board[x][y] = '1';
  39.         queue<Point> qPoint;
  40.         qPoint.push(Point(x,y));
  41.         Point tmpPoint=Point(0,0);
  42.         int xBound = board.size();
  43.         int yBound = board[0].size();
  44.         while (!qPoint.empty())
  45.         {
  46.             tmpPoint = qPoint.front();
  47.             x = tmpPoint.x;
  48.             y = tmpPoint.y;
  49.             if (isInside(x+1, y, xBound, yBound) && board[x+1][y] == 'O')
  50.             {
  51.                 qPoint.push(Point(x+1, y));
  52.                 board[x+1][y] = '1';
  53.             }
  54.             if (isInside(x-1, y, xBound, yBound) && board[x-1][y] == 'O')
  55.             {
  56.                 qPoint.push(Point(x-1, y));
  57.                 board[x-1][y] = '1';
  58.             }
  59.             if (isInside(x, y+1, xBound, yBound) && board[x][y+1] == 'O')
  60.             {
  61.                 qPoint.push(Point(x, y+1));
  62.                 board[x][y+1] = '1';
  63.             }
  64.             if (isInside(x, y - 1, xBound, yBound) && board[x][y - 1] == 'O')
  65.             {
  66.                 qPoint.push(Point(x, y - 1));
  67.                 board[x][y - 1] = '1';
  68.             }
  69.             qPoint.pop();
  70.         }
  71.     }
  72.     bool isInside(int x, int y, int xBound, int yBound)
  73.     {
  74.         return x >= 0 && x < xBound && y >= 0 && y < yBound;
  75.     }
  76.     struct Point
  77.     {
  78.         int x;
  79.         int y;
  80.         Point(int a, int b) :x(a), y(b){}
  81.     };
  82. };