Class Solution

RegionsCutBySlashes.java:1–49

class Solution {
    int rows;
    int cols;
    int dir[][] = {{-1,0},{0,1},{1,0},{0,-1}};
  //visit all nodes of a component using DFS
    public void dfs(int row, int col, int matrix[][]){
        //out of bound, already visited, obstacle
        if(row<0 || row>=rows || col<0 || col>=cols || matrix[row][col]==1){
            return;
        }
        matrix[row][col] = 1;
        for(int i=0;i<4;i++){
            dfs(row + dir[i][0], col + dir[i][1], matrix);
        }
    }
    public int regionsBySlashes(String[] grid) {
        //create a 3*3 grid
        int size = grid.length;
        rows = size*3;
        cols = size*3;
        int matrix[][] = new int[size*3][size*3];
        for(int i=0;i<size;i++){
            for(int j=0;j<size;j++){
                int row = i*3;
                int col = j*3;
                if(grid[i].charAt(j) == '/'){
                    matrix[row][col+2] = 1;
                    matrix[row+1][col+1] = 1;
                    matrix[row+2][col] = 1;
                }else if(grid[i].charAt(j) == '\\'){
                    matrix[row][col] = 1;
                    matrix[row+1][col+1] = 1;
                    matrix[row+2][col+2] = 1;
                }
            }
        }
        int count=0;
        for(int i=0;i<size*3;i++){
            for(int j=0;j<size*3;j++){
                if(matrix[i][j]==0){
                    dfs(i,j,matrix);
                    count++;
                }
            }
        }
        return count;
        
    }
}