Hash Table Concept and Hash Functions in DSA C - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Simple Hash Function Modulo Operation

What is the output of the following code that simulates a hash function using modulo operation on keys?

DSA C

int keys[] = {10, 22, 31, 4, 15};
int size = 10;
for (int i = 0; i < 5; i++) {
    int hash = keys[i] % size;
    printf("%d -> %d\n", keys[i], hash);
}

A

10 -> 0
22 -> 2
31 -> 3
4 -> 4
15 -> 5

B

10 -> 1
22 -> 2
31 -> 3
4 -> 4
15 -> 5

C

10 -> 0
22 -> 2
31 -> 1
4 -> 4
15 -> 5

D

10 -> 0
22 -> 1
31 -> 2
4 -> 3
15 -> 4

💡 Hint

Remember that modulo operation returns the remainder after division.

Each key is divided by the size (10), and the remainder is the hash value. For example, 10 % 10 = 0, 22 % 10 = 2, etc.

🧠 Conceptual

intermediate

Understanding Hash Collisions

Which of the following statements best describes a hash collision in a hash table?

A A key is not found in the hash table.

B Two different keys produce the same hash value.

C The hash function returns a negative number.

D The hash table is empty.

💡 Hint

Think about what happens when two keys map to the same slot.

A hash collision occurs when two distinct keys generate the same hash index, causing them to compete for the same position in the table.

❓ Predict Output

advanced

Output of Hash Function with String Keys

What is the output of this code that calculates a simple hash for strings by summing ASCII values and taking modulo?

DSA C

char* keys[] = {"abc", "bcd", "ace"};
int size = 5;
for (int i = 0; i < 3; i++) {
    int sum = 0;
    for (int j = 0; keys[i][j] != '\0'; j++) {
        sum += keys[i][j];
    }
    int hash = sum % size;
    printf("%s -> %d\n", keys[i], hash);
}

A

abc -> 1
bcd -> 3
ace -> 0

B

abc -> 3
bcd -> 0
ace -> 1

C

abc -> 4
bcd -> 2
ace -> 2

D

abc -> 2
bcd -> 4
ace -> 1

💡 Hint

Calculate ASCII sums carefully, then apply modulo 5.

Sum of ASCII values modulo table size (5): 'abc' (97+98+99=294) % 5 = 4 'bcd' (98+99+100=297) % 5 = 2 'ace' (97+99+101=297) % 5 = 2

🔧 Debug

advanced

Identify the Error in Hash Function Implementation

What error does the following hash function code produce when compiling or running?

DSA C

int hash(char* key, int size) {
    int sum = 0;
    for (int i = 0; key[i] != '\0'; i++)
        sum += key[i];
    return sum / size;
}

int main() {
    char* key = "test";
    int size = 10;
    int h = hash(key, size);
    printf("Hash: %d\n", h);
    return 0;
}

A No error; outputs hash value.

B Runtime error: division by zero if size is zero.

C Syntax error: missing braces in for loop.

D Logical error: uses division instead of modulo, wrong hash output.

💡 Hint

Check the arithmetic operation used to reduce the sum to a hash index.

The function uses division (sum / size) instead of modulo (sum % size), so the hash value is incorrect and may exceed table size.

🧠 Conceptual

expert

Choosing a Good Hash Function Property

Which property is most important for a hash function to minimize collisions in a hash table?

A Uniform distribution of hash values across the table.

B Fast computation time regardless of input size.

C Deterministic output for the same input.

D Ability to handle only numeric keys.

💡 Hint

Think about how keys spread in the hash table.

Uniform distribution ensures keys spread evenly, reducing collisions and improving performance.