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1. Which statements about get(key, t) on the time store are true? Pick all that apply.

Pick every answer that is true.

It returns the newest value whose timestamp is at or before tA value set at exactly time t is visible to get(key, t)It raises KeyError for a key that was never setIt checks every stored version in order, so a long history costs many steps

2. Which statements about the three top-K methods are true? Pick all that apply.

Pick every answer that is true.

A min-heap of size K keeps only K words and costs about u times log K, where u is the number of distinct wordsSorting every distinct word costs more than needed when K is smallThe bucket method needs n + 1 buckets, because one word's count can be as large as nheapq is a max-heap, so pushing each count as it is keeps the K largest

3. What does this program print? ``

python
import bisect

times = [3, 6, 8, 12]
values = ['p', 'q', 'r', 's']

def get(t):
    i = bisect.bisect_right(times, t)
    return '' if i == 0 else values[i - 1]

print('[' + get(2) + ']', get(7), get(11))

``

[p] q r[] q r[] p s[] q s

4. What does this program print? ``

python
from collections import Counter

words = ['cat', 'dog', 'cat', 'emu', 'dog', 'cat']
counts = Counter(words)
entries = sorted(counts.items(), key=lambda e: e[1])
print(entries[0][0], entries[1][0])

`` The counts are cat=3, dog=2 and emu=1.

cat dogdog catemu dogemu cat

5. Why does set refuse a timestamp that is not larger than the last stored timestamp for that key?

Timestamps are int values, and an int cannot repeatThe list of versions must stay in time order, or the binary search returns wrong answersA dict cannot hold two versions for one keyOtherwise get would return an empty string

Time store and top K