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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
思路：从四条边上的‘0‘入手，与其邻接的‘O‘都不被改，记为‘D‘。逆向思维！从不被改的‘O‘入手，而非寻找被改得‘O‘
class Solution { public: void dfs(int x, int y){ if(x<0 || x>=m || y<0 || y>=n || board[x][y]!=‘O‘) return; board[x][y]=‘D‘; //图的四个方向遍历 dfs(x-1,y); dfs(x+1,y); dfs(x,y-1); dfs(x,y+1); } void solve(vector<vector<char>> &board){ if (board.empty()) return; this->board = board; m=board.size(); n=board[0].size(); if(n<=2 || m<=2) return; for(int j=0;j<n;j++){ dfs(0,j); dfs(m-1,j); } for(int i=1;i<m;i++){ dfs(i,0); dfs(i,n-1); } for(int i=0;i<m;i++) for(int j=0;j<n;j++){ if(this->board[i][j]==‘O‘) this->board[i][j]=‘X‘; else if(this->board[i][j]==‘D‘) this->board[i][j]=‘O‘; } board = this->board; } private: int m,n; vector<vector<char>> board; };
130. Surrounded Regions (Graph; DFS)
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原文地址：http://www.cnblogs.com/qionglouyuyu/p/4854717.html
