Financial Ghost Transactions

An audit tool flags 'ghost transactions'. A ghost transaction is any transaction ID that appears again within K steps of its previous occurrence in the ledger. Given a sequence of transaction IDs, count how many instances are flagged as ghosts. Input Format: The first line contains an integer K. The second line contains space-separated transaction ID strings. Output Format: An integer count of ghost transactions. Example: Input: 2 TX1 TX2 TX3 TX1 TX2 TX1 Output: 1 (Explanation: TX1 at index 3 is 3 steps from index 0 [3 > 2]. TX2 at index 4 is 3 steps from index 1 [3 > 2]. TX1 at index 5 is 2 steps from index 3 [2 <= 2]. So only index 5 is a ghost.)