v0.40: Create exercises. Challenge the community.

longest_palindrome

Your mission

Scan a single command-line string and surface the longest contiguous slice that reads the same in both directions.

See it in action

./longest_palindrome "racecar"

Expected result

racecar

Your checklist

For your own tracking. Tests grade your code.

The program expects exactly one argument: the string to inspect.
Find the longest contiguous substring that is identical when read left-to-right and right-to-left.
When several candidates share the maximum length, keep the one whose starting index is the smallest (left-most match wins).
Write the result followed by a newline character.
If the program does not receive exactly one argument (argc must be 2), print wrong number of arguments followed by a newline. If the argument is the empty string, print only a newline.

More examples

./longest_palindrome "abcdcbxyz"

Expected result

bcdcb

./longest_palindrome "shipitlevell"

Expected result

level

./longest_palindrome

Expected result

wrong number of arguments

Constraints

Expected files

longest_palindrome.c

Allowed functions

write

longest_palindrome

Strings: walking and searching

Your mission

Scan a single command-line string and surface the longest contiguous slice that reads the same in both directions.

See it in action

./longest_palindrome "racecar"

Expected result

racecar

Your checklist

For your own tracking. Tests grade your code.

The program expects exactly one argument: the string to inspect.
Find the longest contiguous substring that is identical when read left-to-right and right-to-left.
When several candidates share the maximum length, keep the one whose starting index is the smallest (left-most match wins).
Write the result followed by a newline character.
If the program does not receive exactly one argument (argc must be 2), print wrong number of arguments followed by a newline. If the argument is the empty string, print only a newline.

More examples

./longest_palindrome "abcdcbxyz"

Expected result

bcdcb

./longest_palindrome "shipitlevell"

Expected result

level

./longest_palindrome

Expected result

wrong number of arguments

Constraints

Expected files

longest_palindrome.c

Allowed functions

write

Tests

Run the tests to grade your code

Build your code, then check each test here. Open a result to inspect its output.

Build

01No argumentsWaiting

02Single character is its own palindromeWaiting

03Entire input is an odd-length palindromeWaiting

04Entire input is an even-length palindromeWaiting

05Rejects a non-palindromic prefix before an even palindromeWaiting

06Matching endpoints alone do not form a palindromeWaiting

07Longest palindrome sits inside the stringWaiting

08Earliest match wins when lengths tieWaiting

09Falls back to the first single characterWaiting

10Dev-culture string with embedded palindromeWaiting

longest_palindrome

Your mission

Scan a single command-line string and surface the longest contiguous slice that reads the same in both directions.

See it in action

./longest_palindrome "racecar"

Expected result

racecar

Your checklist

For your own tracking. Tests grade your code.

The program expects exactly one argument: the string to inspect.
Find the longest contiguous substring that is identical when read left-to-right and right-to-left.
When several candidates share the maximum length, keep the one whose starting index is the smallest (left-most match wins).
Write the result followed by a newline character.
If the program does not receive exactly one argument (argc must be 2), print wrong number of arguments followed by a newline. If the argument is the empty string, print only a newline.

More examples

./longest_palindrome "abcdcbxyz"

Expected result

bcdcb

./longest_palindrome "shipitlevell"

Expected result

level

./longest_palindrome

Expected result

wrong number of arguments

Constraints

Expected files

longest_palindrome.c

Allowed functions

write

v0.40: Create exercises. Challenge the community.

Meet Studio →

longest_palindrome

Strings: walking and searching

Your mission

Scan a single command-line string and surface the longest contiguous slice that reads the same in both directions.

See it in action

./longest_palindrome "racecar"

Expected result

racecar

Your checklist

For your own tracking. Tests grade your code.

The program expects exactly one argument: the string to inspect.
Find the longest contiguous substring that is identical when read left-to-right and right-to-left.
When several candidates share the maximum length, keep the one whose starting index is the smallest (left-most match wins).
Write the result followed by a newline character.
If the program does not receive exactly one argument (argc must be 2), print wrong number of arguments followed by a newline. If the argument is the empty string, print only a newline.

More examples

./longest_palindrome "abcdcbxyz"

Expected result

bcdcb

./longest_palindrome "shipitlevell"

Expected result

level

./longest_palindrome

Expected result

wrong number of arguments

Constraints

Expected files

longest_palindrome.c

Allowed functions

write

Tests

Run the tests to grade your code

Build your code, then check each test here. Open a result to inspect its output.

Build

01No argumentsWaiting

02Single character is its own palindromeWaiting

03Entire input is an odd-length palindromeWaiting

04Entire input is an even-length palindromeWaiting

05Rejects a non-palindromic prefix before an even palindromeWaiting

06Matching endpoints alone do not form a palindromeWaiting

07Longest palindrome sits inside the stringWaiting

08Earliest match wins when lengths tieWaiting

09Falls back to the first single characterWaiting

10Dev-culture string with embedded palindromeWaiting