N Queen Problem. Print all solutions for N queen based on either row first order or column first. http://poj.grids.cn/practice/2698/

gistfile1.txt

import java.io.*;
public class Main{

    static PrintWriter pw = new PrintWriter(new OutputStreamWriter(System.out));
    static int N = 8; 
    static int cnt = 0;

    public static void main(String[] args){
        int[] array = new int[N];
        cnt = 0;
        dfs(array, 0);
        pw.close();
    }

    static void dfs(int[] array, int idx){
        if (idx == N){
            output(array, false);
            return;
        }
        for (int i=0; i<N; i++){
            if (isSafe(array, i, idx)){
                array[idx] = i;
                dfs(array, idx+1);
            }
        }
    }

    // check if columnId is a safe position for row[rowId]
    static boolean isSafe(int[] array, int columnId, int rowId){
        for (int i=0; i<rowId; i++){
            if (array[i] == columnId || Math.abs(i - rowId) == Math.abs(array[i] - columnId))
                return false;
        }
        return true;
    }
    static void output(int[] array, boolean rowFirst){
        cnt++;
        pw.println("No. " + cnt);
        for (int i=0; i<N; i++){
            for (int j=0; j<N; j++){
                boolean expr = j == array[i];
                if (!rowFirst)
                    expr = i == array[j];
                if (expr)
                    pw.print("1 ");
                else
                    pw.print("0 ");
            }
            pw.println();
        }
    }
}