Java for LeetCode 225 Implement Stack using Queues

標籤：

Implement the following operations of a stack using queues.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• empty() -- Return whether the stack is empty.

Notes:

• You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, and is empty operations are valid.
• Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
• You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

Update (2015-06-11):
The class name of the Java function had been updated to MyStack instead of Stack.

解題思路：

用Queue的執行個體LinkedList實現，JAVA實現如下：

class MyStack {LinkedList<Integer> queue;MyStack() {this.queue = new LinkedList<Integer>();}// Push element x onto stack.public void push(int x) {queue.add(x);}// Removes the element on top of the stack.public void pop() {queue.remove(queue.size()-1);}// Get the top element.public int top() {return queue.getLast();}// Return whether the stack is empty.public boolean empty() {return queue.isEmpty();}}

 

Java for LeetCode 225 Implement Stack using Queues