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MyQueue.java
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MyQueue.java
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package implementqueueusingstacks;
import java.util.Stack;
/**
* Implement the following operations of a queue using stacks.
* <p>
* 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:
* <p>
* MyQueue queue = new MyQueue();
* <p>
* queue.push(1);
* queue.push(2);
* queue.peek(); // returns 1
* queue.pop(); // returns 1
* queue.empty(); // returns false
* Notes:
* <p>
* 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).
*/
/**
* 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();
*/
public class MyQueue {
Stack<Integer> stack1;
Stack<Integer> stack2;
/** Initialize your data structure here. */
public MyQueue() {
stack1 = new Stack<>();
stack2 = new Stack<>();
}
/** Push element x to the back of queue. */
public void push(int x) {
while (!stack1.empty()) {
stack2.push(stack1.pop());
}
stack1.push(x);
while (!stack2.empty()) {
stack1.push(stack2.pop());
}
}
/** Removes the element from in front of queue and returns that element. */
public int pop() {
return stack1.pop();
}
/** Get the front element. */
public int peek() {
return stack1.peek();
}
/** Returns whether the queue is empty. */
public boolean empty() {
return stack1.empty();
}
}
/*
Details
Runtime: 0 ms, faster than 100.00% of Java online submissions for Implement Queue using Stacks.
Memory Usage: 37.1 MB, less than 6.25% of Java online submissions for Implement Queue using Stacks.
*/