Page Comparison

func solveNQueens(n int) (result [][]string) {
    solve(&result, n, newBoard(n), 0)
    return
}

func solve(result *[][]string, n int, board [][]byte, row int) {
    if row == n {
        *result = append(*result, flat(board))
        return
    }
    
    for col := 0; col < n; col++ {
        if !isValid(board, row, col) {
            continue
        }
        
        board[row][col] = 'Q'
        
        solve(result, n, board, row+1)
        
        board[row][col] = '.'
    }
}

func isValid(board [][]byte, row, col int) bool {
    n := len(board)
    
    for i := 0; i <= row; i++ {
		if board[i][col] == 'Q' {
			return false
		}
	}
    for i, j := row-1, col+1; i >= 0 && j < n; i, j = i-1, j+1 {
		if board[i][j] == 'Q' {
			return false
		}
	}
    for i, j := row-1, col-1; i >= 0 && j >= 0; i, j = i-1, j-1 {
		if board[i][j] == 'Q' {
			return false
		}
	}
    
    return true
}

func newBoard(n int) [][]byte {
    board := make([][]byte, n)
    for i := range board {
        board[i] = bytes.Repeat([]byte("."), n)
    }
    return board
}

func flat(board [][]byte) []string {
    result := make([]string, len(board))
    for i := range result {
        result[i] = string(board[i])
    }
    return result
}

func totalNQueens(n int) (result int) {
    solve(&result, n, newBoard(n), 0)
    return
}

func solve(result *int, n int, board [][]byte, row int) {
    if row == n {
        (*result)++
        return
    }
    
    for col := 0; col < n; col++ {
        if !isValid(board, row, col) {
            continue
        }
        
        board[row][col] = 'Q'
        
        solve(result, n, board, row+1)
        
        board[row][col] = '.'
    }
}

func isValid(board [][]byte, row, col int) bool {
    n := len(board)
    
    for i := 0; i <= row; i++ {
		if board[i][col] == 'Q' {
			return false
		}
	}
    for i, j := row-1, col+1; i >= 0 && j < n; i, j = i-1, j+1 {
		if board[i][j] == 'Q' {
			return false
		}
	}
    for i, j := row-1, col-1; i >= 0 && j >= 0; i, j = i-1, j-1 {
		if board[i][j] == 'Q' {
			return false
		}
	}
    
    return true
}

func newBoard(n int) [][]byte {
    board := make([][]byte, n)
    for i := range board {
        board[i] = bytes.Repeat([]byte("."), n)
    }
    return board
}