String Reversal Approaches in DSA C - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of string reversal using two-pointer swap

What is the output of the following C code that reverses a string using two pointers swapping characters?

DSA C

void reverse(char *str) {
    int left = 0;
    int right = strlen(str) - 1;
    while (left < right) {
        char temp = str[left];
        str[left] = str[right];
        str[right] = temp;
        left++;
        right--;
    }
}

int main() {
    char s[] = "hello";
    reverse(s);
    printf("%s", s);
    return 0;
}

A olleh

B hello

C ohlle

D Syntax error

💡 Hint

Think about swapping characters from start and end moving towards the center.

The code swaps characters from the start and end moving inward, reversing the string 'hello' to 'olleh'.

❓ Predict Output

intermediate

Output of string reversal using recursion

What is the output of this C code that prints a string in reverse using recursion?

DSA C

#include <stdio.h>
void reversePrint(char *str) {
    if (*str == '\0') return;
    reversePrint(str + 1);
    putchar(*str);
}

int main() {
    char s[] = "abc";
    reversePrint(s);
    return 0;
}

A abc

B cba

C Syntax error

D Runtime error

💡 Hint

The function calls itself with the next character before printing the current one.

The recursion goes to the end of the string, then prints characters on the way back, reversing the output.

🧠 Conceptual

advanced

Why is in-place reversal more memory efficient?

Which reason best explains why reversing a string in-place (modifying the original string) is more memory efficient than creating a new reversed string?

A It uses a linked list internally

B It compresses the string during reversal

C It avoids allocating extra memory for a new string copy

D It uses recursion which saves memory

💡 Hint

Think about memory allocation for new data versus modifying existing data.

In-place reversal changes the original string without needing extra space for another string, saving memory.

🔧 Debug

advanced

Identify the error in this string reversal code

What error does this C code produce when trying to reverse a string literal?

DSA C

void reverse(char *str) {
    int left = 0;
    int right = strlen(str) - 1;
    while (left < right) {
        char temp = str[left];
        str[left] = str[right];
        str[right] = temp;
        left++;
        right--;
    }
}

int main() {
    char *s = "hello";
    reverse(s);
    printf("%s", s);
    return 0;
}

A Segmentation fault (runtime error)

B Compilation error

C Output: olleh

D No output

💡 Hint

String literals are stored in read-only memory in C.

The code tries to modify a string literal which is stored in read-only memory, causing a runtime crash.

🚀 Application

expert

Result of reversing a palindrome string in-place

Given the string "madam", what is the state of the string after applying an in-place reversal function?

A Syntax error

B madma

C madam\0

D madam

💡 Hint

A palindrome reads the same forwards and backwards.

Reversing a palindrome string results in the same string because it reads identically both ways.