Currency Conversion from Logs | Dataford Interview Questions

Amazon Pay receives currency conversion rates as directed exchange relationships. Given a log of known rates, implement a function that converts an amount from any source currency to a target currency, possibly through intermediate currencies.

Formal Specification

Implement convert_currency(rates, source, target, amount), where rates is a list of records [from_currency, to_currency, rate]. Each rate means one unit of from_currency equals rate units of to_currency. The function must return the converted amount as a floating-point number. Every rate is positive. You may use the reciprocal rate to convert in the opposite direction. Return -1.0 if no conversion path exists. Converting a currency to itself returns the original amount.

Use graph traversal to find a path and multiply the rates along that path. You may assume that a valid path, when one exists, does not require revisiting a currency.

Constraints

1 <= len(rates) <= 10^4
Currency codes are non-empty uppercase strings of length at most 5
0 < rate <= 10^6
0 <= amount <= 10^12
The graph may contain disconnected components
A valid path does not require revisiting a currency

Function Signature

def convert_currency(rates, source, target, amount):

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Problem