L9 Hw3 1

def interleaved_sum(n, odd_func, even_func):
    """Compute the sum odd_func(1) + even_func(2) + odd_func(3) + ..., up
    to n.

    >>> identity = lambda x: x
    >>> square = lambda x: x * x
    >>> triple = lambda x: x * 3
    >>> interleaved_sum(5, identity, square) # 1   + 2*2 + 3   + 4*4 + 5
    29
    >>> interleaved_sum(5, square, identity) # 1*1 + 2   + 3*3 + 4   + 5*5
    41
    >>> interleaved_sum(4, triple, square)   # 1*3 + 2*2 + 3*3 + 4*4
    32
    >>> interleaved_sum(4, square, triple)   # 1*1 + 2*3 + 3*3 + 4*3
    28
    >>> from construct_check import check
    >>> check(HW_SOURCE_FILE, 'interleaved_sum', ['While', 'For', 'Mod']) # ban loops and %
    True
    >>> check(HW_SOURCE_FILE, 'interleaved_sum', ['BitAnd', 'BitOr', 'BitXor']) # ban bitwise operators, don't worry about these if you don't know what they are
    True
    """
    def helper(k,n,odd_func, even_func):
        # 利用n区分递归的Base和递进
        if k<=n:
            return odd_func(k)+helper2(k+1,n,odd_func,even_func)
        else:
            return 0
    def helper2(k,n,odd_func, even_func):
        if k<=n:
            return even_func(k)+helper(k+1,n,odd_func,even_func)
        else:
            return 0

    return helper(1,n,odd_func,even_func)

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