leetcode 128: Surrounded Regions

Surrounded RegionsFeb 22976 / 3801

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 XX O O XX X O XX O X X

After running your function, the board should be:

X X X XX X X XX X X XX O X X

java:

class Solution {    public void solve(char[][] board) {        if(board==null || board.length<=2) return;        if(board[0]==null || board[0].length<=2) return;                int m = board.length;        int n = board[0].length;        Queue<Pair> queue = new LinkedList<Pair>();                for(int i=0; i<m; i++) {            for(int j=0; j<n; j++) {                if(board[i][j] == 'O') {                    if(i==0 || i==m-1 || j==0 || j==n-1) {                        queue.offer( new Pair(i,j) );                    } else board[i][j] = 'P';                }            }        }                while(!queue.isEmpty() ) {            Pair p = queue.poll();            int x = p.x;            int y = p.y;                        if( x-1>0 && board[x-1][y] =='P' ) {                board[x-1][y] = 'O';                queue.offer( new Pair(x-1,y) );            }            if( x+1<m && board[x+1][y] =='P' ) {                board[x+1][y] = 'O';                queue.offer( new Pair(x+1,y) );            }            if( y-1>0 && board[x][y-1] =='P' ) {                board[x][y-1] = 'O';                queue.offer( new Pair(x,y-1) );            }            if( y+1<n && board[x][y+1] =='P' ) {                board[x][y+1] = 'O';                queue.offer( new Pair(x,y+1) );            }        }                for(int i=0; i<m; i++) {            for(int j=0; j<n; j++) {                if(board[i][j] == 'P') board[i][j] = 'X';            }        }    }    class Pair{         int x;        int y;        public Pair(int x, int y) {            this.x = x;            this.y = y;        }    }}

c++:

class Solution {public:    void solve(vector<vector<char>> &board) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        int m = board.size();        if(m<1) return;                int n = board[0].size();                queue<pair<int,int>> que;        set<pair<int,int>> unique;                for(int i=0; i<n; i++) {            if(board[0][i]=='O') {                board[0][i] = 'S';                que.push( make_pair(0,i) );            }                        if(board[m-1][i]=='O') {                board[m-1][i] = 'S';                que.push( make_pair(m-1,i) );            }        }                for(int i=1; i<m-1; i++) {            if(board[i][0]=='O') {                board[i][0] = 'S';                que.push( make_pair(i,0) );            }                        if(board[i][n-1]=='O') {                board[i][n-1] = 'S';                que.push( make_pair(i, n-1) );            }        }                while(!que.empty()){            pair<int,int> p = que.front();            que.pop();            for(int i=-1; i<=1; i++) {                for(int j=-1; j<=1; j++) {                    if(p.first+i<0 || p.first+i>m-1 || p.second+j<0 || p.second+j>n-1 || (abs(i+j)!=1) ) continue;                                        char & c = board[p.first+i][p.second+j];                    pair<int,int> index = make_pair(p.first+i, p.second+j);                    if(c=='O' && unique.find(index) == unique.end() ) {                        que.push(index);                        unique.insert(index);                        c = 'S';                    }                }            }        }                for(int i=0; i<m; i++) {            for(int j=0; j<n; j++) {                if(board[i][j] == 'S') {                    board[i][j] = 'O';                } else if( board[i][j] == 'O') {                    board[i][j] = 'X';                }            }        }    }};