Create Statistics endpoint

[maria-farooq]

GET /statistics

This is the main endpoint of this task, this endpoint have to execute in constant time and
memory (O(1)). It returns the statistic based on the transactions which happened in the last 60
seconds.

Returns:
{
"sum": 1000,
"avg": 100,
"max": 200,
"min": 50,
"count": 10
}

Where:
● sum is a double specifying the total sum of transaction value in the last 60 seconds
● avg is a double specifying the average amount of transaction value in the last 60
seconds
● max is a double specifying single highest transaction value in the last 60 seconds
● min is a double specifying single lowest transaction value in the last 60 seconds
● count is a long specifying the total number of transactions happened in the last 60
seconds

Requirements

For the rest api, the biggest and maybe hardest requirement is to make the GET /statistics
execute in constant time and space. The best solution would be O(1). It is very recommended to
tackle the O(1) requirement as the last thing to do as it is not the only thing which will be rated in
the code challenge.