Free Practice Quiz Question List

7 Hash Tables Online Quiz Questions

Use this free practice quiz with 20 questions to review 7 Hash Tables, test your knowledge, and prepare for your next test or exam.

20 questions

Choose one

1 point

Which goal best describes the primary purpose of a hash table?

A
It maintains all keys in sorted order.
B
It locates keys quickly using hashing.
C
It guarantees logarithmic worst-case lookup.
D
It eliminates the need for key equality checks.

Choose all

1 point

Which two statements about hashing and key equality are correct? Select all that apply.

A
Equal keys must have equal hash values.
B
Unequal keys can never have the same hash value.
C
A collision-resolution strategy may be needed.
D
A hash value alone proves that two keys are equal.

Written response

1 point

In open addressing, what is the technical name for a marker placed in a deleted slot so that later searches continue probing?

Fill in the blank

1 point

The collision-resolution strategy in which each bucket refers to a collection of entries is called .

Choose all

1 point

Which two effects are generally associated with increasing a hash table's load factor? Select all that apply.

A
It generally reduces lookup costs.
B
It generally increases chain or probe lengths.
C
It always makes the table use less memory overall.
D
It can save space while making operations more expensive.

Written response

1 point

A separate-chaining table stores 15 entries in 20 buckets. What is its load factor? Enter the decimal value.

Fill in the blank

1 point

When a hash table grows to a larger array, it its existing entries because the bucket indices may change.

Choose one

1 point

Which statement correctly describes resizing and insertion complexity when a hash table grows geometrically?

A
One resize costs O(n), but geometric growth can make insertion O(1) amortized.
B
Every insertion costs O(n) because the table may eventually resize.
C
A resize costs O(1) because entries keep their old numerical indices.
D
Geometric growth guarantees O(log n) worst-case insertion.

True or false

1 point

Deleting an entry from an open-addressed table by marking its slot completely empty can make a later search incorrectly report that another key is absent.

A
True
B
False

Open ended

1 point

Explain when a hash table is a better choice than a balanced search tree, and when the balanced search tree is preferable. Contrast their relevant performance and ordering properties.

Choose one

1 point

Which pair of disadvantages is specifically associated with separate chaining?

A
It cannot store more entries than its number of buckets.
B
It may incur pointer or allocation overhead and poorer cache locality.
C
It requires a tombstone for every deletion.
D
It guarantees that all searches take O(1) worst-case time.

Choose one

1 point

A hash table uses separate chaining, and two different keys map to bucket 3. How are the two entries normally stored?

A
Each colliding entry is discarded except the first
B
All entries are stored in the bucket's chain
C
Every collision immediately doubles the table
D
The key is converted into a sorted-tree node

Choose one

1 point

Which statement correctly describes the relationship between key equality and hashing?

A
Unequal keys must always have different hash values
B
Equal keys may have different hash values if their buckets match
C
Equal keys must have equal hash values, while unequal keys may still collide
D
A hash value alone proves that two keys are equal

Choose one

1 point

A chained hash table contains 18 entries distributed across 6 buckets. What is its load factor $\alpha = \frac{n}{m}$ ?

A
3
B
$\frac{1}{3}$
C
6
D
24

Choose one

1 point

Why does an open-addressed hash table commonly use a tombstone when deleting an entry?

A
It permanently reserves the slot for the deleted key
B
It causes every key in the table to be rehashed immediately
C
It marks the slot as occupied by a new replacement entry
D
It marks a deleted slot so probing continues during searches

Choose one

1 point

A hash table grows from 4 buckets to 8 buckets and uses $index = hash(key) \bmod m$ . Why must existing entries be rehashed?

A
The key values themselves must be changed to fit the new array
B
The bucket index may change when the modulus changes
C
Only entries involved in collisions need a new hash value
D
Rehashing is needed only when the table shrinks

True or false

1 point

True or false: If a hash table doubles its capacity when a threshold is reached, insertion can be amortized $O(1)$ even though one insertion that triggers resizing may cost $O(n)$ .

A
True
B
False

Written response

1 point

What term names the formation of long contiguous runs of occupied slots caused by linear probing?

Written response

1 point

What property should a key have while stored in a hash table so that its hash value and equality behavior do not change unexpectedly?

True or false

1 point

True or false: In an open-addressed hash table with $m=10$ , the table can correctly support insertions at load factor $\alpha=1$ as long as each probe sequence examines every slot.

A
True
B
False