//
//  main.swift
//  EightQueens
//
//  Created by Donald Burr on 5/27/15.
//  Copyright (c) 2015 Donald Burr. All rights reserved.
//

import Foundation

var solutionsFound = 0
var positionsChecked = 0

// create 8 queen objects, place them one per row
let myQueens = map(0...7) { Queen(forRow: $0) }

func isSafe(currentRow: Int, currentColumn: Int) -> Bool {
    positionsChecked++
    
    // iterate over all queens in previous rows
    for previousRow in 0..<currentRow {
        // check vertical: are we trying to place in the same column as a previously placed queen?
        if myQueens[previousRow].column == currentColumn {
            return false
        }
        // check diagonal
        let differenceInRows = currentRow - previousRow
        let differenceInColumns = currentColumn - myQueens[previousRow].column
        if (differenceInRows == differenceInColumns || differenceInRows == -differenceInColumns) {
            return false
        }
    }
    
    // compared all previous queens, no conflict
    myQueens[currentRow].column = currentColumn
    return true
}

func moveQueenAcrossRow(row: Int) {
    for column in 0...7 {
        // move queen column by column, checking if it's safe
        if isSafe(row, column) {
            // if we just placed the 8th queen, we have a result!
            if row == 7 {
                solutionsFound++
                printAnswer()
            } else {
                // recursive call - now move the queen to the NEXT row
                moveQueenAcrossRow(row+1)
            }
        }
    }
}

func printAnswer() {
    println("SOLUTION #\(solutionsFound)")
    println()
    
    // go backwards to print from top down
    for currentRow in reverse(0...7) {
        // print row number (using chess numbering)
        print(currentRow+1)
        for currentColumn in 0...7 {
            if (myQueens[currentRow].column == currentColumn) {
                print(" Q ")
            } else {
                print(" . ")
            }
        }
        println()
    }
    println("  A  B  C  D  E  F  G  H  ")
    println()
}

// start by trying to move queen across row 0
moveQueenAcrossRow(0)

// that's it
println("POSITIONS CHECKED: \(positionsChecked)")