我如何从这段代码中删除回溯？

def fibonacci(n):
    fib = [0, 1] + [0] * (n - 1)
    for i in range(2, n + 1):
        fib[i] = fib[i - 1] + fib[i - 2]
    return fib[n]

def fibonacci(n):
    a, b = 0, 1
    for _ in range(n):
        a, b = b, a + b
    return a

def is_valid(board, row, col):
    # 检查同一列是否有重复
    for x in range(row):
        if board[x][col] == 1:
            return False

    # 检查左上对角线
    for x, y in zip(range(row, -1, -1), range(col, -1, -1)):
        if board[x][y] == 1:
            return False

    # 检查右上对角线
    for x, y in zip(range(row, -1, -1), range(col, len(board))):
        if board[x][y] == 1:
            return False

    return True

def solve_n_queens(board, row):
    if row == len(board):
        return True

    for col in range(len(board)):
        if is_valid(board, row, col):
            board[row][col] = 1
            if solve_n_queens(board, row + 1):
                return True
            board[row][col] = 0

    return False

def fibonacci(n, memo={}):
    if n in memo:
        return memo[n]
    if n <= 1:
        return n
    memo[n] = fibonacci(n - 1, memo) + fibonacci(n - 2, memo)
    return memo[n]