NQueens benchmark

using System;
using System.Collections.Generic;

public class NQueens {

    public class Position {
        int x;
        int y;

        public Position(int i, int j) {
            x = i;
            y = j;
        }

        public bool canPlace(Position other) {
            return x != other.x && y != other.y && Math.Abs(x - other.x) != Math.Abs(y - other.y);
        }

        public String toString() {
            return "(" + x + "," + y + ")";
        }
    }

    public static Position position(int i, int j) {
        return new Position(i, j);
    }

    public bool isValid(Position prospect, List<Position> solution) {
        foreach (Position position in solution) {
            if (!prospect.canPlace(position)) {
                return false;
            }
        }
        return true;
    }

    public List<Position> nextColPositions(int col, int n, List<Position> solution) {
        List<Position> ret = new List<Position>();
        Position temp;
        for (int i = 0; i < n; i++) {
            temp = position(i, col);
            if (isValid(temp, solution)) {
                ret.Add(temp);
            }
        }
        return ret;
    }

    public List<List<Position>> solve(int col, int n, List<List<Position>> solutions) {
        List<List<Position>> result = new List<List<Position>>();
        if (col >= n) {
            return solutions;
        } else {
            List<Position> prospects;
            List<Position> temp = null;
            foreach (List<Position> solution in solutions) {
                prospects = nextColPositions(col, n, solution);
                foreach (Position p in prospects) {
                    temp = new List<Position>(solution);
                    temp.Add(p);
                    result.Add(temp);
                }
                solution.Clear();
            }
            solutions.Clear();
            return solve(col + 1, n, result);
        }
    }

    public void nqueens(int n) {
        List<List<Position>> input = new List<List<Position>>();
        input.Add(new List<Position>());
        List<List<Position>> solutions = solve(0, n, input);
        Console.WriteLine("No. of Solutions for n = " + n + " : " + solutions.Count);
    }

    public static void Main(string[] args) {
        int n = 13;
        for (int i = 0; i <= n; i++) {
            var timer = System.Diagnostics.Stopwatch.StartNew();
            new NQueens().nqueens(i);
            timer.Stop();
            Console.WriteLine("Time taken(ms) : " + timer.ElapsedMilliseconds);
        }
        Console.WriteLine("Poop");
    }
}