Implement Stack using Queues

1import java.util.Queue;
2import java.util.LinkedList;
3
4// one-queue approach
5// enqueue O(n)
6// dequeue O(1)
7class MyStack {
8    Queue<Integer> queue;
9
10    public MyStack() {
11        queue = new LinkedList<Integer>();
12    }
13    
14    public void push(int x) {
15        int currentSize = queue.size();
16        queue.offer(x);
17        // Shift by the previous number of elements
18        for (int i = 0; i < currentSize; i++) {
19            queue.offer(queue.poll());
20        }
21    }
22    
23    public int pop() {
24        return queue.poll();
25    }
26    
27    public int top() {
28        return queue.peek();
29    }
30    
31    public boolean empty() {
32        return queue.isEmpty();
33    }
34}
35
36// enqueue O(1)
37// dequeue O(n)
38// class MyStack {
39//     Queue<Integer> queue1;
40//     Queue<Integer> queue2;
41
42//     public MyStack() {
43//         queue1 = new LinkedList<Integer>();
44//         queue2 = new LinkedList<Integer>();
45//     }
46    
47//     public void push(int x) {
48//         queue1.offer(x);
49//     }
50    
51//     public int pop() {
52//         while (queue1.size() > 1) {
53//             queue2.offer(queue1.poll());
54//         }
55//         int popped = queue1.poll();
56//         Queue<Integer> temp = queue1;
57//         queue1 = queue2;
58//         queue2 = temp; 
59//         return popped;
60//     }
61    
62//     public int top() {
63//         while (queue1.size() > 1) {
64//             queue2.offer(queue1.poll());
65//         }
66//         int theTop = queue1.peek();
67//         queue2.offer(queue1.poll());
68//         Queue<Integer> temp = queue1;
69//         queue1 = queue2;
70//         queue2 = temp; 
71//         return theTop;
72//     }
73    
74//     public boolean empty() {
75//         return queue1.isEmpty();
76//     }
77// }
78
79// enqueue O(n)
80// dequeue O(1)
81// class MyStack {
82//     Queue<Integer> queue1;
83//     Queue<Integer> queue2;
84
85//     public MyStack() {
86//         queue1 = new LinkedList<Integer>();
87//         queue2 = new LinkedList<Integer>();
88//     }
89    
90//     public void push(int x) {
91//         queue2.offer(x);
92//         while (!queue1.isEmpty()) {
93//             queue2.offer(queue1.poll());
94//         }
95//         Queue<Integer> temp = queue1;
96//         queue1 = queue2;
97//         queue2 = temp; 
98//     }
99    
100//     public int pop() {
101//         return queue1.poll();
102//     }
103    
104//     public int top() {
105//         return queue1.peek();
106//     }
107    
108//     public boolean empty() {
109//         return queue1.isEmpty();
110//     }
111// }
112
113/**
114 * Your MyStack object will be instantiated and called as such:
115 * MyStack obj = new MyStack();
116 * obj.push(x);
117 * int param_2 = obj.pop();
118 * int param_3 = obj.top();
119 * boolean param_4 = obj.empty();
120 */