Describe how to implement a queue using two stacks. Show how to implement the ‘d
ID: 3905867 • Letter: D
Question
Describe how to implement a queue using two stacks. Show how to implement the ‘dequeue()’ method. based on the following implementation of the ‘enque()’ method. What is the worst-case complexity of your ‘dequeue()’ implementation?
Queue Q1, Q2; // assume you start with two empty queues
void push (Item X) {
Q1.enqueue(X);
}
Item pop( ) { // add comments to explain your idea
}
Complexity of your pop() implementation:
Explanation / Answer
Hello Student!
I am happy to help you!
The question says that we need to implement a queue using two stacks. So, why would we need two queues queue 1 and 2. I think there is a slight mistake in the explanation. It must be two stacks.
Coming over to the code :
stack<Item> s1, s2;
void enqueue(Item value) {
// Push the value in stack s1
s1.push(value);
}
Item dequeue() {
// If S2 is empty
if(s2.isEmpty()) {
// if s1 is also empty therefpre there is no element in the stack.
if(s1.isEmpty()) {
// return -1 if there is no element in both of the stacks
return -1;
}
// push all the elements into other stack such that it reverses the order
while(!s1.isEmpty()) {
s2.push(s1.pop());
}
}
// pop s2.
return s2.pop();
}
Complexity of pop operation will be O(n)
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