-
Notifications
You must be signed in to change notification settings - Fork 0
/
ImplementQueueUsingStack.java
42 lines (35 loc) · 1.05 KB
/
ImplementQueueUsingStack.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
import java.util.Stack;
public class ImplementQueueUsingStack {
private Stack<Integer> stack1;
private Stack<Integer> stack2;
/** Initialize your data structure here. */
public ImplementQueueUsingStack() {
stack1 = new Stack<Integer>();
stack2 = new Stack<Integer>();
}
/** Push element x to the back of queue. */
public void push(int x) {
stack1.push(x);
}
/** Removes the element from in front of queue and returns that element. */
public int pop() {
if(stack2.empty())
while(!stack1.empty())
stack2.push(stack1.pop());
return stack2.pop();
}
/** Get the front element. */
public int peek() {
if(this.empty()) return -1;
if(stack2.empty())
while(!stack1.empty())
stack2.push(stack1.pop());
int res = stack2.pop();
stack2.push(res);
return res;
}
/** Returns whether the queue is empty. */
public boolean empty() {
return stack1.empty() && stack2.empty();
}
}