Question

My lecturer has supplied some pseudocode in his course notes for the n-Queens problem. Unfortunately I’m having a bit of a hard time understanding it to do an implementation in Java. The pseudocode in question is:

Queens (currentBoard , currentRow, n) :
    if currentRow == n:
        if currentBoard is legal:
            return <currentBoard, 1>
        else:
            return <currentBoard, 0>
    else:
        for k = 1..n:
            newBoard = currentBoard + <currentRow+1, k>
            board [k], success[k] = Queens(newBoard, currentRow+1, n)
        kmax = index of max(success[k])
        return <board[kmax], success[kmax]>

Most of it I understand but I’m not sure what I’m meant to do with the parts of the pseudocode that are in the angle brackets.

Answer 1

The angle brackets here just say, that multiple “objects” are returned.

So, for example, this code

return <currentBoard, 1>

returns on the one hand the currentBoard object and on the other hand a simple 1.

In this code

board [k], success[k] = Queens(newBoard, currentRow+1, n)

you can see that both objects are stored into different variables, to board goes into board[k] and the number goes into success[k].