« Reverse a Queue

Reverse Queue

You have been given a queue that can store integers as the data. You are required to write a function that reverses the populated queue itself without using any other data structures.

Input Format:

The first list of input contains an integer 't' denoting the number of test cases/queries to be run. Then the test cases follow.

The first line input for each test case/query contains an integer N, denoting the total number of elements in the queue.

The second line of input contains N integers separated by a single space, representing the order in which the elements are enqueued into the queue. Output Format: For each test case/query, the only line of output prints the order in which the queue elements are dequeued, all of them separated by a single space.

Output for every test case/query will be printed on a new line.

Note:

You are not required to print the expected output explicitly, it has already been taken care of. Just make the changes in the input queue itself.

Constraints:

1 <= t <= 100

1 <= N <= 10^4

-2^31 <= data <= 2^31 - 1

Time Limit: 1sec

Sample Input 1:

1

6

1 2 3 4 5 10

Note:

Here, 1 is at the front and 10 is at the rear of the queue.

Sample Output 1:

10 5 4 3 2 1

Sample Input 2:

2

5

2 8 15 1 10

3

10 20 30

Sample Output 2:

10 1 15 8 2

30 20 10

Copy
1#include <iostream>
2using namespace std;
3
4#include<queue>
5
6void reverseQueue(queue<int> &input) {
7    // Write your code here
8    if(input.size() == 0){
9        return;
10    }
11
12    int top = input.front();
13    input.pop();
14    reverseQueue(input);
15    input.push(top);
16}
17
18int main() {
19    int t;
20    cin >> t;
21
22    while (t--) {
23        queue<int> q;
24        int size;
25        cin >> size;
26
27        for (int i = 0, val; i < size; i++) {
28            cin >> val;
29            q.push(val);
30        }
31
32        reverseQueue(q);
33        while (!q.empty()) {
34            cout << q.front() << " ";
35            q.pop();
36        }
37
38        cout << "\n";
39    }
40}