Nsryjdtyk

I am new to JAVA. Below is my code of NQueens problem. The results are [[Ljava.lang.String;@123a439b, [Ljava.lang.String;@7de26db8].

Can anyone please help? Thank you very much! I copyied the code from other's blog. The code should be correct. I just don't know how to print out the results. I think this should be not very hard. My background is not computer science, that's maybe why I have the trouble. Thank you!

import java.util.ArrayList;





public class Solution {

public ArrayList<String> solveNQueens(int n) {

    ArrayList<String> res = new ArrayList<String>();

    if(n<=0)

        return res;



    int  columnVal = new int[n];



    DFS_helper(n,res,0,columnVal);



    return res;

}



public void DFS_helper(int nQueens, ArrayList<String> res, int row, int columnVal){

    if(row == nQueens){

        String unit = new String[nQueens];

        for(int i = 0; i < nQueens; i++){

            StringBuilder s = new StringBuilder();

            for(int j = 0; j < nQueens; j++){

                if(j == columnVal[i])

                    s.append("Q ");

                else

                    s.append("+ ");

            }



            unit[i] = s.toString();

            //System.out.println(unit[i]);



        }



        //System.out.println();



        res.add(unit);



      // System.out.println(Arrays.toString(res));

       //return;

    }



    else{

        for(int i = 0; i < nQueens; i++){

            columnVal[row] = i;//(row,columnVal[row)==>(row,i)



            if(isValid(row,columnVal))

                DFS_helper(nQueens, res, row+1, columnVal);

        }

    }

}



public boolean isValid(int row, int  columnVal){

    for(int i = 0; i < row; i++){

        if(columnVal[row] == columnVal[i]

           ||Math.abs(columnVal[row]-columnVal[i]) == row-i)

           return false;

    }

    return true;

}





public static void main(String args) {

    Solution su = new Solution();

    int n = 4;



    System.out.println(su.solveNQueens(n));

}

}

While you do System.out.println(su.solveNQueens(n)); it prints list contents which are array and it just prints array object, but not it's contents. so, to print array contents you need to iterate through them.

Arrays.toString Returns a string representation of the contents of the specified array. 

https://docs.oracle.com/javase/7/docs/api/java/util/Arrays.html#toString(java.lang.Object)

get result into a list and then print it:

List<String> res = su.solveNQueens(n);

for(String strs : res) {

            System.out.println(Arrays.toString(strs));

}

You can do like this too as the above prints with ,. Here iterating through the list and then array.

List<String> res = su.solveNQueens(n);

for(String strs : res) {

        for(String s: strs) {

            System.out.print(s+ " ");

        }

        System.out.println();

    }

in java 8, you can make use of stream and lambda:

ArrayList<String> result = su.solveNQueens(n)

result.stream().forEach(i->System.out.println(Arrays.toString(i)));