33. Checksum Validation

You are given a block of memory (array of n bytes) which includes n-1 data bytes and the last byte as checksum.

Your task is to verify whether the last byte equals the XOR of all previous bytes (excluding itself).

Return:

• 1 if the checksum is valid
• 0 if the checksum is incorrect

Checksum: It’s a simple error-detection method that ensures data hasn’t been corrupted during storage or transmission.

The sender calculates based on specific algorithm and sends it with the data; the receiver recalculates it similarly from the received data—if both match, the data is intact, otherwise it’s likely corrupted.

Some methods used are 

• Simple Sum Add all bytes, keep only the lowest 8 or 16 bits.
• XOR Checksum: XOR all bytes of data.
• CRC (Cyclic Redundancy Check): more accurate, etc
   

Example-1

Input: n = 5, mem = [10, 20, 30, 40, 60]
Output: 1

(XOR = 10 ^ 20 ^ 30 ^ 40 = 60)

Example-2

Input: n = 4, mem = [5, 9, 1, 3]
Output: 0

(XOR = 5 ^ 9 ^ 1 = 13, checksum = 3)

Example-3

Input: n = 3, mem = [7, 3, 4]
Output: 1

(XOR = 7 ^ 3 = 4)