Question$4(10$ points$)$

Another pattern is found to be critical for the communication of the above servers. This pattern is CDA, and your task is to count how many times servers used this pattern in a fragment of their communication. Your function takes a string patch and outputs how many CDA $s$ occurred in the patch.

Contract

contract: countPattern: patch$($string$)$ number

Examples

$($check$-$expect $($countPattern "BACCDACBABBCCABCCDABDADCDAABC"$)3)$

$($check$-$expect $($countPattern "ACACCDAACDAAAABBCCDACCCDCAABD"$)3)$

$($check$-$expect $($countPattern "BCACDABCDDCACDBDDBDCACDBCDABC"$)2)$You can only use this List of available functionS