CS61A Homework 1

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Homework 1: Variables & Functions, Control hw01.zip

Parsons Problems

Q2: k in Num

Write a function k_in_num which takes in two integers, k and num. k_in_num returns True if num has the digit k and returns False if num does not have the digit k. 0 is considered to have no digits.

def k_in_num(k, num):
    """
    Complete k_in_num, a function which returns True if num has the digit k and
    returns False if num does not have the digit k. 0 is considered to have no
    digits.

    >>> k_in_num(3, 123) # .Case 1
    True
    >>> k_in_num(2, 123) # .Case 2
    True
    >>> k_in_num(5, 123) # .Case 3
    False
    >>> k_in_num(0, 0) # .Case 4
    False
    """
    "*** YOUR CODE HERE ***"
    Construct your solution here, including indents

def k_in_num(k, num):
    while num:
        if k == num % 10:
            return True
        num = num // 10
    return False

Code Writing Problems

Q3: A Plus Abs B

Python’s operator module defines binary functions for Python’s intrinsic arithmetic operators. For example, calling operator.add(2,3) is equivalent to calling the expression 2 + 3; both will return 5.

Fill in the blanks in the following function for adding a to the absolute value of b, without calling abs. You may not modify any of the provided code other than the two blanks.

def a_plus_abs_b(a, b):
    """Return a+abs(b), but without calling abs.

    >>> a_plus_abs_b(2, 3)
    5
    >>> a_plus_abs_b(2, -3)
    5
    >>> a_plus_abs_b(-1, 4)
    3
    >>> a_plus_abs_b(-1, -4)
    3
    """
    if b < 0:
        f = _____
    else:
        f = _____
    return f(a, b)

    if b < 0:
        f = sub
    else:
        f = add
    return f(a, b)

Q4: Two of Three

Write a function that takes three positive numbers as arguments and returns the sum of the squares of the two smallest numbers. Use only a single line for the body of the function.

def two_of_three(i, j, k):
    """Return m*m + n*n, where m and n are the two smallest members of the
    positive numbers i, j, and k.

    >>> two_of_three(1, 2, 3)
    5
    >>> two_of_three(5, 3, 1)
    10
    >>> two_of_three(10, 2, 8)
    68
    >>> two_of_three(5, 5, 5)
    50
    """
    return _____
    return i * i + j * j + k * k - max(i, j, k) * max(i, j, k)

Hint: Consider using the max or min function:

>>> max(1, 2, 3)
3
>>> min(-1, -2, -3)
-3

Q5: Largest Factor

Write a function that takes an integer n that is greater than 1 and returns the largest integer that is smaller than n and evenly divides n.

def largest_factor(n):
    """Return the largest factor of n that is smaller than n.

    >>> largest_factor(15) # factors are 1, 3, 5
    5
    >>> largest_factor(80) # factors are 1, 2, 4, 5, 8, 10, 16, 20, 40
    40
    >>> largest_factor(13) # factor is 1 since 13 is prime
    1
    """
    "*** YOUR CODE HERE ***"
    res = 1
    for i in range(2, n):
        if n % i == 0:
            res = n // i
            break
    return res 

Hint: To check if b evenly divides a, you can use the expression a % b == 0, which can be read as, “the remainder of dividing a by b is 0.”