CompSci 101 Fall 2020, Exam 2 Solutions

Problem 2.1 Part A
result = [w for w in food if w.count('a') == 1]
OR
result = [w for w in food if sum([1 for x in w if x=='a']) == 1]

Problem 2.2 Part B
result = [w for w in words if 'a' in w[:int(len(w)/2)]]
OR
print("a in first half", result)

Problem 2.3 Part C
result = [w for w in set(list1)&set(list2)]
OR
result = list(set(list1)&set(list2))
OR
result = [w for w in set(list1) if w in set(list2)]
OR
result = list(set([w for w in list1 if w in list2]))
OR
result = list(set(list1).intersection(set(list2)))

Problem 2.4 Part D
result = list(set(list1)^set(list2))
OR
result = [w for w in set(list1)^set(list2)]
OR
result = list(set(list1).symmetric_difference(set(list2)))
OR
result = list(set(list1)-set(list2)) + list(set(list2)-set(list1))
OR
list(set([w for w in list1 if w not in list2]+[w for w in list2 if w not in list1]))

Problem 2.5 Part E
result = a[b.index(max(b))]
OR
result = [a[i] for i in range(len(a)) if b[i] == max(b)][0]
OR
result = [x for x in a if a.index(x) == b.index(max(b))][0]
OR
dict = {}
for idx in range(len(b)):
    dict[a[idx]] = b[idx]
final = sorted(dict.items(), key = lambda x:x[1])
result = final[-1][0]

Problem 2.6 Part F
result = sorted([x for x in d])
OR
result = sorted(d.keys())
OR
result = [a[0] for a in sorted(d.items(), key = lambda x:x[0])]

Problem 2.7 Part G
result = sorted(set([x for x in d.values()]))
OR
result = sorted([x for x in set(d.values())])
OR
result = sorted(set(d.values()))
OR
result = [x for x in sorted(set(d.values()))]
OR
result = sorted(list(set(d.values())))

Problem 2.8 Part H
result = sum([len(d[x]) for x in d.keys()])
OR
result = sum([len(d[x]) for x in d])
OR
result = sum([len(x) for x in d.values()])

Problem 3

Here is a correct solution

def isAlpha(letter):
    return letter in "abcdefghijklmnopqrstuvwxyz"

def processScores(data):
    answer = []
    index = 0
    name = ""
    nums = []
    first = True
    while index<len(data):
        if isAlpha(data[index][0]):
            if not first:   # found another one
                answer.append((name, sum(nums)/len(nums)))
            else: # first one
                first = False
            name = data[index]
            nums = []
        else:    # number
            nums.append(float(data[index]))
        index += 1
    answer.append((name, sum(nums) / len(nums)))
    return sorted(answer, key=lambda x:x[1], reverse=True)

There are two errors.

1) mention that the tuple ('junyang', 78.75) was not added to answer.

To fix this the last tuple needs to be appended after the while loop.

    answer.append((name, sum(nums) / len(nums)))

2) The list is not sorted

To fix this the last line above sorts on the second item in each tuple in
reverse order.

    return sorted(answer, key=lambda x:x[1], reverse=True)

Problem 4.1 Part A

def howMuchSpent(data, name):
    amount = 0
    for lst in data:
        if lst[1] == name:
            amount += float(lst[2])
    return amount

Problem 4.2 Part B

def uniqueGamesWon(data, name):
    answer = set([])       # answer = set()   ok too
    for lst in data:
        if lst[1] == name and lst[3] == 'won':
            answer.add(lst[0])
    return sorted(answer)

OR

    ans = []
    for line in data:
	if line[1] == name:
            if line[3] == 'won':
                ans.append(line[0])
    return sorted(set(ans))

Problem 4.3 Part C

def checkdata(data):
    d = {}
    for lst in data:
        if lst[0] not in d:
            d[lst[0]] = lst[2]
        elif d[lst[0]] != lst[2]:
            print("Error in price", lst[0] )
OR

    d = {}
    for lst in data:
        if lst[0] not in d:
            d[lst[0]] = set()
        d[lst[0]].add(lst[2])
    for k,v in d.items():
        if len(v) > 1:
            print("Error in " + k)

OR

d = {}
    for line in data:
        if line[0] not in d:
            d[line[0]] = []
        d[line[0]].append(line[2])
    for key in d:
        if len(set(d[key])) != 1:
            print('Error in price', key)

OR

 dict = {}
    for x in data:
        if x[0] not in dict:
            dict[x[0]] = set([x[2]])
        else:
            dict[x[0]].add(x[2])
    list =[w[0] for w in dict.items() if len(w[1])>=2]
    for i in list:
        print('Error in ' + i)

Problem 4.4 Part D


def dictNamesToListAnimals(data):
    d = {}
    for lst in data:
        if lst[3] == "won":
            if lst[1] not in d:
                d[lst[1] ] = []
            d[lst[1]].append(lst[4])
    return d

OR

def dictNamesToListAnimals(data):
    d = {}
    for lst in data:
        if lst[1] not in d and lst[3] == 'won':
            d[lst[1]] = [lst[-1]]
        elif lst[1] in d and lst[3] == 'won'':
            d[lst[1]].append(lst[-1])
    return d

OR

def dictNamesToListAnimals(data):
    d = {} 
    for lst in data: 
        if len(lst) == 5: 
            if lst[1] not in d: 
                d[lst[1]] = [lst[4]]
            else: 
                d[lst[1]] += [lst[4]]    # must be a list if adding to list
    return d

OR

def dictNamesToListAnimals(data):
    d = {}
    for lst in data:
        if len(lst) > 4:
            person = lst[1]
            animal = lst[-1]
            if person not in d:
                d[person] = []
            d[person].append(animal)
    return d

Problem 4.5 Part E

def animalWon(dname, numtimes):
    d = {}
    for name in dname:
        for animal in dname[name]:
            if animal not in d:
                d[animal] = 0
            d[animal] += 1
    answer = [key  for key in d if d[key] == numtimes ]
    return sorted(answer)


OR

def animalWon(dname, numtimes):
    d = {}
    for player in dname:
        for animal in dname[player]:
            if animal not in d:
                d[animal] = 0
            d[animal] += 1

    result = [x for x, y in d.items() if y == numtimes]
    return sorted(result)

OR


def animalWon(dname, numtimes):
    d = {}
    lst = []
    for alist in dname.values():
        for animal in alist:
            if animal not in d:
                d[animal] = 0
            d[animal] += 1
    for key in d:
        if d[key] == numtimes:
            lst.append(key)
    return sorted(lst)
	
OR

def animalWon(dname, numtimes):
    animals = []
    for list in dname.values(): 
        for animal in list: 
            animals.append(animal) 

    unique = set(animals) 
    ret = []
    for animal in unique: 
        if animals.count(animal) == numtimes: 
            ret.append(animal)
    return sorted(ret)

OR

def animalWon(dname, numtimes):
    ret = []
    animals = dname.values()
    animal_lst = []
    for element in animals:
        animal_lst += element     # adding list to list
    animal_unique = set(animal_lst)
    for a in animal_unique:
        n = animal_lst.count(a)
        if n == numtimes:
            ret.append(a)
    return sorted(ret)

OR

def animalWon(dname, numtimes):
    lst = []
    answer = []
    for lst2 in dname.values():
        lst += lst2
    for item in lst:
        if lst.count(item) == numtimes and item not in answer:
            answer.append(item)
    return sorted(answer)

Problem 4.6 Part F

def wonMostPrizes(data):
    d= {}
    for lst in data:
        if lst[3] == "won":
            if lst[1] not in d:
                d[lst[1]] = []
            d[lst[1]].append(lst[4])
    print("dict built")
    maxnum = max([len(d[key]) for key in d])
    answer = [(key, sorted(d[key])) for key in d if len(d[key]) == maxnum]
    return answer[0]

OR

def wonMostPrizes(data):
    d = dictNamesToListAnimals(data)
    maxnum = max([len(d[key]) for key in d])
    answer = [(key, sorted(d[key])) for key in d if len(d[key]) == maxnum]
    return answer[0]

OR

def wonMostPrizes(data):
    d = dictNamesToListAnimals(data) 
    high = 0 
    winner = ''
    for person in d: 
    if len(d[person]) > high: 
        high = len(d[person])
        winner = person 
   ret = (winner, sorted(d[winner])) 
   return ret