python 斐波那契数列

def fibonacci_recursive(n):
    if n <= 0:
        return 0
    elif n == 1:
        return 1
    else:
        return fibonacci_recursive(n-1) + fibonacci_recursive(n-2)

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

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

def fibonacci_memoization(n, memo={}):
    if n in memo:
        return memo[n]
    if n <= 0:
        return 0
    elif n == 1:
        return 1
    memo[n] = fibonacci_memoization(n-1, memo) + fibonacci_memoization(n-2, memo)
    return memo[n]