Stacks and Queues

Queue Enqueue/Dequeue

Enqueue values at the back and dequeue them from the front in first-in, first-out order.

Algorithm

The replay uses the same three values in every language, so this R DSA implementation can be compared directly with the rest of the DSA track.

Basic Implementation

basic.R 
render <- function(values) {
  paste(values, collapse = " -> ")
}

queue <- c()
for (value in c(10, 20, 30)) queue <- c(queue, value)
removed <- c()
while (length(queue) > 0) {
  removed <- c(removed, queue[1])
  queue <- queue[-1]
}
cat(render(removed), "\n", sep = "")

Complexity

  • Time: O(1) per operation with a real queue
  • Space: O(n)

Implementation notes

  • Keep the explicit stack/queue operations. Library shortcuts that only produce the final list hide the data-structure behavior this lesson is meant to replay.
  • The final output uses a deterministic a -> b -> c format for cross-language comparison.
front The front is the oldest value still waiting in the queue.
FIFO A queue removes values in first-in, first-out order.