Number of Transactions per Visit

You are given two tables represented as arrays:

• visits, where each row is [user_id, visit_date], representing that user_id visited the bank on visit_date.
• transactions, where each row is [user_id, transaction_date, amount], representing that user_id made one transaction of amount on transaction_date.

For each visit, count how many transactions the same user_id made on that exact visit date. Then compute a histogram where:

• transactions_count is a possible number of transactions made during a visit.
• visits_count is the number of visits that had exactly transactions_count transactions.

Return the histogram as a list of [transactions_count, visits_count] pairs sorted by transactions_count in ascending order.

You must include every transactions_count from 0 through the maximum number of transactions made in any single visit. If no visit had a particular transaction count, its visits_count should be 0.