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Thread: recursion to find a solution for K queen problem (variation)

  1. #1
    Junior Member
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    Dec 2018
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    Default recursion to find a solution for K queen problem (variation)

    I'm trying to write a function that can take a partial solution to a problem and give a solution. I am given a board of size MxN , where I should attempt to place K queens given a partial solution of K'

    for example the following board:

    Q X * *
    * * Q *
    * * X *
    * * X *

    the function should take this board, and the indexes 1 for row and 2 for column, the current number of queens on it - 2 and the final number of queens to be on it - 4. I'm only allowed to add queens on the rowth row from the colth column to the end of that row, and any following row for any column in this example - (1,3), (2,0), (2,1), (2,2), (2,3), (3,0), (3,1), (3,2), (3,3) the function should print true because it is possible .. for example the following:

    Q X * *
    * * Q *
    * * X *
    * Q X Q

    however my function doesn't quite do that and I can't see why..

    private static boolean kQueens(int[][] board, int k, int row, int col, int numOfQueens) {
            if (numOfQueens == k) return true;
            //trying to place a queen in the row at the col+1 ~ row length position.
            // if possible place it and try to place a new one in the next position.
            for (int i = 0; i < board.length; ++i) {
                for (int j = 0; j < board[i].length; j++) {
                    //save the value of that position in case we'll need to change it back
                    int tmp = board[i][j];
                    if (addQueen(board, i, j)) {
                        board[i][j] = QUEEN;
                    if (kQueens(board, k, i, j, numOfQueens + 1)) {
                        return true;
                   //remove the queen and backtrack
            return false;
    Last edited by lidor718; December 5th, 2018 at 12:16 PM.

  2. #2
    Super Moderator Norm's Avatar
    Join Date
    May 2010
    Eastern Florida
    Thanked 2,635 Times in 2,585 Posts

    Default Re: recursion to find a solution for K queen problem (variation)

    Please edit your post and wrap your code with code tags:


    to get highlighting and preserve formatting.

    Please post the output from the program that shows what you are talking about. Add some comments to locate the problems.
    If you don't understand my answer, don't ignore it, ask a question.

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