codestep

# HW 04

# Q1: Weights

def planet(size):
    """Construct a planet of some size."""
    assert size > 0
    return ['planet', size]

def size(w):
    """Select the size of a planet."""
    assert is_planet(w), 'must call size on a planet'
    return w[1]
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# Q2: Balanced

    if is_planet(m):
        return True
    return length(left(m)) * total_weight(end(left(m))) == length(right(m)) * total_weight(end(right(m))) and balanced(end(left(m))) and balanced(end(right(m)))
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# Q3: Totals

    if is_planet(m):
        return [size(m)]
    return [total_weight(m), totals_tree(end(left(m))), totals_tree(end(right(m)))]
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# Trees

# Q4: Replace Leaf

    if is_leaf(t) and old == label(t):
            return tree(replacement)
    return tree(label(t),[replace_leaf(branch,old,replacement) for branch in branches(t)])
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# Q5: Password Protected Account

注意尝试三次后账号将被锁定！

    try_pwds = []
    def withdraw(amount, pas):
        nonlocal balance
        if len(try_pwds) >= 3:
            return "Your account is locked. Attempts: " + str(try_pwds)
        if password != pas:
            try_pwds.append(pas)
            return 'Incorrect password'
        if amount > balance:
           return 'Insufficient funds'
        balance = balance - amount
        return balance
    return withdraw
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# Q6: Joint Account

其实在 withdraw 函数上加限制条件就好了。

    account = withdraw(0, old_pass)
    if type(account) == str:
        return account
    def joint(money, pwd):
        if pwd == new_pass or pwd == old_pass:
            return withdraw(money, old_pass)
        return withdraw(money, pwd)
    return joint
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# Extra Questions

下面是一些区间方面的函数抽象。

# Q7: Interval Abstraction

注意格式。

答案：interval.py

代码实现：

def lower_bound(x):
    return x[0]

def upper_bound(x):
    return x[1]
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# Q8: Sub Interval

答案：mul_interval.py 。

# Q9: Div Interval

div_interval.py

# Q11: Quadratic

    point = -b/(2*a)
    point_val =  a*point*point + b*point + c
    lower_val = a*lower_bound(x)*lower_bound(x)+ b*lower_bound(x) + c
    upper_val = a*upper_bound(x)*upper_bound(x)+ b*upper_bound(x) + c
    if point > lower_bound(x) and point < upper_bound(x):
        return interval(min(lower_val,upper_val,point_val), max(lower_val,upper_val,point_val))
    else:
        return interval(min(lower_val,upper_val), max(lower_val,upper_val))
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← Lab 06 →