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Multiple servers have access to a single variable (think of some sort of unique ID. Each access will increment the variable) How to design the system to ensure the iniquity of the variable?

Querying a user table that has fields of first name, last name, and so on. How to make a select statement fast on the first name, that is "where first_name = ?". And what data type shall be used? (I was totally lost on the second part of this question)

Given an integer array, construct another integer array whose i-th element is the sum of i-th element and following i elements. For example,a given [3, 6, 2, 7, 9, 5, 4, 1], the output array is [3, 8 (6+2), 18 (2+7+9), 25 (7+9+5+4), 19 (9+5+4+1)]

You have an integer array. Starting from arr[startIndex], follow each element to the index it points to. You continue to do this until you find a cycle. Return the length of the cycle. If no cycle is found return -1

forexample {1, 0}, 0) => 2
{1, 2, 0}, 0) => 3

As we all know that poker cards have four suites: Spades, Hearts, Clubs and Diamonds with figures from 1 to 13.
Now you are given a set of poker cards, you can pick any one card as the first card. And except for the first card, you can only pick the card that has the same suit or figure with the previous one.
Return the max number of cards you can.
For example: [(H, 3), (H, 4), (S, 4), (D, 5), (D, 1)], it returns 3 as follows: (H,3)-->(H,4)-->(S,4)