Serve the First K Customers in Line
Practice using a queue (Queue/Deque) to process items in first-in, first-out order.
Customers are waiting in a line, given as an array line where line[0] is at the front. Simulate a queue: serve customers from the front, one at a time, until you've served k of them or the line is empty. Return the customer IDs in the order they were served.
This is a basics exercise for queues (Queue/ArrayDeque in Java, Queue<T> in C#, collections.deque in Python, an array used with shift/push in JS/TS) — first-in, first-out (FIFO) processing.
Example 1
Input: line = [101,102,103,104], k = 2
Output: [101,102]
Explanation: The first 2 customers in line are served in order.
Example 2
Input: line = [5], k = 3
Output: [5]
Explanation: Only 1 customer exists, so only 1 is served.
Example 3
Input: line = [7,8,9], k = 0
Output: []
Constraints
- 0 <= line.length <= 1000
- 0 <= k <= 1000
Follow-up
How would you implement a queue using two stacks instead of a built-in Queue type?
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