N Queens

public class NQueens {
    NQueens(int num){
        n=num;
    }
    static int count1=0;
    static int n;
    static int []grid = new int[20];
    static boolean[]visited_col = new boolean[30];
    static boolean[]diag_right = new boolean[50];
    static boolean[]diag_left = new boolean[50];
    private static void SolveQueen(int row) {
     int loopLimit=n;
    if(row ==0)
    {
        loopLimit = n/2;
    }
    for(int col = 0; col < loopLimit; col++){
    if(!visited_col[col] && !diag_right[row+col] && !diag_left[n+col-row]){
        grid[row] = 1;
        visited_col[col] = true;
        diag_right[col+row] = true;
        diag_left[n+col-row] = true;
    if(row==n-1)
        count1++;
    else
        SolveQueen(row+1);
        grid[row] = 0;
        visited_col[col] = false;
        diag_right[col+row] = false;
        diag_left[n+col-row] = false;
    }
    }
    }
    int count(){
        SolveQueen(0);
        return count1*2;
    }
}