Suppose you have a big text log file and there are three columns:

Name City Timestamp
John city1 t4
Bob city1 t3
John city2 t1
John city3 t3
Bob city3 t2
John city4 t2
Bob city4 t1

The first column is a driver name, the second is a city name, and the final is a timestamp (32-bit integer).
This log file maintains a history of drivers.
We define a "triple" as a tuple of three consecutive cities a driver has been to that are ordered by timestamp.

Suppose t1 < t2 < t3 < t4, then we will have the following triples:
for John, we have: (city2, city4, city3), (city4, city3, city1)
for Bob, we have: (city4, city3, city1)

Write a program to output all the triples in the file and for each triple,

output the count of unique drivers that have been to that triple.

For the example input, the output would be

(city2, city4, city3) 1

(city4, city3, city1) 2