//Enter any number between 3 and 9 to get the solution... //code created by Seniru Pasan Indira for the N-Queens Problem on 1/19/2019 3:00PM /** * All known BUGS: * the code throws an ArraysIndexOutOfBoundsException when the dimension is set to more than 8 - therefore a method call with dimension provided more than 8 is not encouraged. */ //importing necessary packages import java.io.*; import java.util.*; import java.util.stream.*; public class ProtectedQueens { static int DIM; //returns all attackable positions a queen could attack public static int[][] getAttackingPositions(int ...coords) { var copy = Arrays.copyOf(coords, coords.length); //arraylist for storing vertical terrotories var up = new ArrayList(); //arraylist for storing horizontal territories var horizontal = new ArrayList(); //arraylist for storing diagonals var diagonals = new ArrayList(); //adding horizontal and vertical territories to arraylists for(int c=0,r=0;cDIM) break; } //returning distinct elements of arraylist containing territories which are converted to an array return Stream.concat(diagonals.stream(),Stream.concat(up.stream(), horizontal.stream())).distinct().toArray(int[][]::new); } public static String[][] getProtectedCoords(int dim) throws Exception { if(dim<4) {throw new Exception("No solutions for the given dimension "+dim);} else if(dim>8) {throw new Exception("Sorry! Not supported!");} //creating variables DIM = dim; int queens; String[][] board; var bigQC = 0; var bigQR = 0; do { //looping until there are enough queens placed in the board board = new String[DIM][DIM]; var owned = new ArrayList(); //switching rows by 1 if column count is greater than the dim if(bigQC>=DIM) {bigQR++;bigQC=0;} //adding attacking positions of the queen in a position Arrays.stream(getAttackingPositions(bigQR,bigQC)).forEach( x->{ if(!owned.contains(x)) { owned.add(x); } }); //placing the first queen board[bigQR][bigQC++] = "Q"; queens = 1; for(var r=0;r{ if(!owned.contains(x)) { owned.add(x); } }); } } } } while (queens!=DIM&&bigQR<=DIM); //returning the board containing queens' coordinates data return board; } //the newContains method as the existing one checks for the memory addresses public static boolean newContains(ArrayList al, int[] arr) { for (var i = 0; i < al.size(); i++) { if (Arrays.equals(arr, al.get(i))) { return true; } } return false; } //main method public static void main(String[] a) { OutputStreamWriter w; Random rand = new Random(); DIM = new Scanner(System.in).nextInt(); //program start time var start = System.currentTimeMillis(); try { //setting the charset for the output stream w = new OutputStreamWriter(System.out,"unicode"); w.write("Solution for "+DIM+" * "+DIM+" board with "+DIM+" queens:\n"); //storing the board var ans = getProtectedCoords(DIM); for(var r=0;r