Join tables to map userId to name

Problem

You are given three tables represented as 2D string arrays (each row is a record, no headers). You need to produce a mapping from userId → customerName by matching and joining information across tables.

Table 1: customers

Each row: [customerName, email, productName, quantity]

• quantity is an integer in string form.
• Assumption: each customer buys only one type of product (i.e., one productName per customer).

Table 2: orders

Each row: [userId, email, orderTotal]

• orderTotal is a number in string form (integer or decimal).
• email may be null (or an empty string, depending on how the input is represented).

Table 3: products

Each row: [productName, unitPrice]

• unitPrice is a number in string form.

Matching / Join requirement

For each order record, identify which customer placed it, then output userId -> customerName.

Use these matching rules:

1. If orders.email is present (non-null/non-empty), match the customer by email.
2. If orders.email is missing, match by using the fact that:

• orderTotal = quantity * unitPrice for the customer’s purchased product.
• Use customers.productName joined to products.productName to get unitPrice.

Output

Return a mapping/dictionary from userId to customerName for all orders.

Assumptions / Edge cases

• If multiple customers could match an order (e.g., same computed total), specify and implement a deterministic tie-breaker (e.g., pick lexicographically smallest name) or return all candidates—clarify with the interviewer.
• Assume inputs are well-formed aside from possible null/empty emails.