problem-solving/Python/fibonacci.py at master · moogacs/problem-solving · GitHub

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#Recursive Method
def Fibonacci(n):
    if n<0:
        print("Incorrect input")
    # First Fibonacci number is 0
    elif n==1:
        return 0
    # Second Fibonacci number is 1
    elif n==2:
        return 1
    else:
        return Fibonacci(n-1)+Fibonacci(n-2)


#Dynamic Programming using Memoization
fib=[0,1]
def Fibonacci1(n):
    if n<0:
        print("Incorrect input")
    # First Fibonacci number is 0
    elif n==1:
        return fib[0]
    # Second Fibonacci number is 1
    elif n==2:
        return fib[1]
    else:
        for i in range(2,n):
            fib.append(fib[-1]+fib[-2])
        return fib[-1]


#Dynamic Programming - Space Optimised
def Fibonacci2(n):
    a = 0
    b = 1
    if n < 0:
        print("Incorrect input")
    # First Fibonacci number is 0
    elif n==1:
        return a
    # Second Fibonacci number is 1
    elif n==2:
        return b
    else:
        for i in range(2,n):
            c = a + b
            a = b
            b = c
        return b