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Hardware interview practice

Bounded byte-string palindrome check

EasyFirmware & ValidationC

A firmware diagnostic receives a byte buffer and length; the bytes are not NUL-terminated. Write the C function that reports whether the buffer reads the same forward and backward.

Starting point

Question code

bool is_palindrome(const uint8_t *p, size_t n);
Reviewed example

Work through one case

Input
p=NULL and n=0.
Expected output
Return true.

The empty byte sequence is a palindrome, and the function handles that case before dereferencing p or computing n-1.

What to cover

Requirements

  1. Return true for lengths zero or one; p may be NULL only when n is zero.
  2. For n greater than zero, return false if p is NULL.
  3. Compare byte values exactly, including zero bytes, and do not modify the buffer.
  4. Run in O(n) time with O(1) extra storage and avoid index underflow for n=0.
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