回溯——N皇后

/**
 * Created by witness on 15-9-26.
 */
public class Queen {
    public static void nQueen(int N, int x, int[] trace){
        for (int i = 0; i < N; i++){
            if (place(trace, x, i)){
                trace[x] = i;
                if (x == N - 1){
                    for (int j = 0; j < N; j++){
                        System.out.print(trace[j] + " ");
                    }
                    System.out.println("");
                } else {
                    nQueen(N, x + 1, trace);
                    trace[x] = 0;
                }
            }
        }
    }
    private static boolean place(int[] trace, int x, int y){
        for (int i = 0; i < x; i++){
            if (trace[i] == y || (trace[i] - i) == (y - x) || trace[i] + i == x + y){
                return false;
            }
        }
        return true;
    }
    public static void main(String[] args){
        int[] trace = new int[8];
        nQueen(8, 0, trace);
    }
}