N Queens II

Follow up for N-Queens problem.

Now, instead outputting board configurations, return the total number of distinct solutions.

Solution:

public class Solution {
    Set<Integer> col = new HashSet<>();
    Set<Integer> diag1 = new HashSet<>();
    Set<Integer> diag2 = new HashSet<>();
    public int totalNQueens(int n) {
        return solve(0, n, 0);
    }
    public int solve(int row, int n, int count){
        if(row==n) return count+1;
        for(int c=0; c<n; c++){
            if(col.contains(c) || diag1.contains(row+c) || diag2.contains(row-c)) continue;
            col.add(c);
            diag1.add(row+c);
            diag2.add(row-c);
            count = solve(row+1,n, count);
            col.remove(c);
            diag1.remove(row+c);
            diag2.remove(row-c);
        }
        return count;
    }
}