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C++ Program to Implement Stack Using Two Queues
Stack
The stack which is implemented as LIFO, where insertion and deletion are done from the same end, top. The last element that entered is deleted first.
Stack operations are −
- push (int data) − Insertion at top
- int pop() − Deletion from top
Queue
The queue which is implemented as FIFO where insertions are done at one end (rear) and deletions are done from another end (front). The first element that entered is deleted first.
Queue operations are −
- EnQueue (int data) − Insertion at the rear end
- int DeQueue() − Deletion from front end
This is a C++ Program to Implement Stack Using Two Queues
Algorithms
Begin function enqueue1 to insert item a at qu1: Set, np1 = new qu1 np1->d1 = a np1->n1 = NULL if (f1 == NULL) Then set r1 = np1 r1->n1 = NULL f1 = r1 else r1->n1 = np1 r1 = np1 r1->n1 = NULL End Begin function dequeue1 to delete item from qu1. if queue is null Print no elements present in queue. Else q1 = f1 f1 = f1->n1 a = q1->d1 delete(q1) return a End Begin function enqueue2 to insert item a at qu2. np2 = new qu2; np2->d2 = a; np2->n2 = NULL; if queue is null Set r2 = np2 r2->n2 = NULL f2 = r2 Else Set r2->n2 = np2 r2 = np2 r2->n2 = NULL End Begin function dequeue2 to delete item from qu2: if queue is null Print no elements present in queue. Else q2 = f2 f2 = f2->n2 a = q2->d2 delete(q2) return a End
Example Code
#include<iostream>
using namespace std;
struct qu1// queue1 declaration {
qu1 *n1;
int d1;
}*f1 = NULL, *r1 = NULL, *q1 = NULL, *p1 = NULL, *np1 = NULL;
struct qu2// queue2 declaration {
qu2 *n2;
int d2;
}*f2 = NULL, *r2 = NULL, *q2 = NULL, *p2 = NULL, *np2 = NULL;
void enqueue1(int a) {
np1 = new qu1;
np1->d1 = a;
np1->n1 = NULL;
if (f1 == NULL) {
r1 = np1;
r1->n1 = NULL;
f1 = r1;
} else {
r1->n1 = np1;
r1 = np1;
r1->n1 = NULL;
}
}
int dequeue1() {
int a;
if (f1 == NULL) {
cout<<"no elements present in queue\n";
} else {
q1 = f1;
f1 = f1->n1;
a = q1->d1;
delete(q1);
return a;
}
}
void enqueue2(int a) {
np2 = new qu2;
np2->d2 = a;
np2->n2 = NULL;
if (f2 == NULL) {
r2 = np2;
r2->n2 = NULL;
f2 = r2;
} else {
r2->n2 = np2;
r2 = np2;
r2->n2 = NULL;
}
}
int dequeue2() {
int a;
if (f2 == NULL) {
cout<<"no elements present in queue\n";
} else {
q2 = f2;
f2 = f2->n2;
a = q2->d2;
delete(q2);
return a;
}
}
int main() {
int n, a, i = 0;
cout<<"Enter the number of elements to be entered into stack\n";
cin>>n;
while (i < n) {
cout<<"enter the element to be entered\n";
cin>>a;
enqueue1(a);
i++;
}
cout<<"\n\nElements popped\n\n";
while (f1 != NULL || f2 != NULL)// if both queues are not null {
if (f2 == NULL)// if queue 2 is null {
while (f1->n1 != NULL) {
enqueue2(dequeue1());
}
cout<<dequeue1()<<endl;
} else if (f1 == NULL)//if queue 1 is null {
while (f2->n2 != NULL) {
enqueue1(dequeue2());
}
cout<<dequeue2()<<endl;
}
}
}Output
Enter the number of elements to be entered into stack 5 enter the element to be entered 1 enter the element to be entered 2 enter the element to be entered 3 enter the element to be entered 4 enter the element to be entered 5 Elements popped 5 4 3 2 1
Updated on: 30-Jul-2019
826 Views
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