A201/A597 Introduction to Programming I (4/3 cr.)

First Summer 2006

Lecture Notes Twenty-Four: Discussing the Solutions for Homework Seven.

Here are the solutions for the problems in Homework Seven:

def scalarProduct(a, b):
    sum = 0
    for i in range(len(a)):
        sum += a[i] * b[i]
    return sum

print scalarProduct([1, -1, 2], [2, 0, 1])

If we test this it produces a 4, which is correct.

We can now move to the second problem, alternatingSum:

def alternatingSum(a):
    sum = 0
    for i in range(len(a)):
        if i % 2 == 0:
            sum = sum + a[i]
        else:
            sum = sum - a[i]
    return sum

print alternatingSum([1, 4, 9, 16, 9, 7, 4, 9, 11])

The next method can reverse a list of numbers:

def reverse(a):
    result = []
    for e in a:
        result.insert(0, e)
    return result

print reverse([1, 2, 3, 4, 5, 6])

Next problem is easy:

def equals(a, b):
    return a == b

But, of course, we didn't mean it that way:

def equals(a, b):
    if len(a) != len(b):
        return False
    else:
        for i in range(len(a)):
            if a[i] != b[i]:
                return False
        return True

print [1, 2] == [2, 1]
print [1, 2] == [1, 2, 1]
print [1, 2] == [1, 2]

Next problem (and the one that follows) have been posted on What's New? for Jun 8:

def sameSet(a, b):
    for i in range(len(a)):
        if not a[i] in b:
            return False
    for elem in b:
        if not contains(a, elem):
            return False
    return True

def contains(a, elem):
    for e in a:
        if e == elem:
            return True
    return False

Here's then the last one:

def sameElements(a, b): # other approach sort then equals
    for e in a:
        if count(e, a) != count(e, b):
            return False
    for e in b:
        if count(e, a) != count(e, b):
            return False
    return True

def count(elem, a):
    sum = 0
    for i in a:
        if i == elem:
            sum += 1
    return sum

With this we're ready for the Practical Exam (and, soon, for the Final Exam as well).

Last updated: June 11, 2006 by Adrian German for A201/A597