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ImplementQueueUsingStacks232.java
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81 lines (69 loc) · 2.21 KB
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/**
* Implement the following operations of a queue using stacks.
*
* push(x) -- Push element x to the back of queue.
* pop() -- Removes the element from in front of queue.
* peek() -- Get the front element.
* empty() -- Return whether the queue is empty.
*
* Example:
*
* MyQueue queue = new MyQueue();
*
* queue.push(1);
* queue.push(2);
* queue.peek(); // returns 1
* queue.pop(); // returns 1
* queue.empty(); // returns false
*
* Notes:
*
* You must use only standard operations of a stack -- which means only push to
* top, peek/pop from top, size, and is empty operations are valid.
* Depending on your language, stack may not be supported natively. You may
* simulate a stack by using a list or deque (double-ended queue), as long as
* you use only standard operations of a stack.
* You may assume that all operations are valid (for example, no pop or peek
* operations will be called on an empty queue).
*/
public class ImplementQueueUsingStacks232 {
class MyQueue {
private Stack<Integer> st;
/** Initialize your data structure here. */
public MyQueue() {
this.st = new Stack<Integer>();
}
/** Push element x to the back of queue. */
public void push(int x) {
Stack<Integer> temp = new Stack<>();
int preSize = this.st.size();
for (int i=0; i<preSize; i++) {
temp.push(this.st.pop());
}
this.st.push(x);
for (int i=0; i<preSize; i++) {
this.st.push(temp.pop());
}
}
/** Removes the element from in front of queue and returns that element. */
public int pop() {
return this.st.pop();
}
/** Get the front element. */
public int peek() {
return this.st.peek();
}
/** Returns whether the queue is empty. */
public boolean empty() {
return this.st.isEmpty();
}
}
}
/**
* Your MyQueue object will be instantiated and called as such:
* MyQueue obj = new MyQueue();
* obj.push(x);
* int param_2 = obj.pop();
* int param_3 = obj.peek();
* boolean param_4 = obj.empty();
*/