之前刷题发现自己对于栈的理解不是很好,所以开一篇文章来写栈。
题目
1.用栈实现队列
题目链接
先来一张队列与栈的图来区分下二者。
下图为本题的详细题解。
class MyQueue {
//存储数据,栈底就是队列的首
Stack<Integer>stack1;
//用来中转数据
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) {
//stack1没有的话可以直接插入。
if(stack1.empty())
{
stack1.push(x);
return ;
}
while(!stack1.empty())
stack2.push(stack1.pop());
stack2.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();
}
}
/**
* 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();
*/
2.用队列实现栈
class MyStack {
Queue<Integer>queue1;
Queue<Integer>queue2;
/** Initialize your data structure here. */
public MyStack() {
queue1 = new LinkedList<>();
queue2 = new LinkedList<>();
}
/** Push element x onto stack. */
public void push(int x) {
if(queue1.isEmpty())
{
queue1.add(x);
return;
}
queue2.add(x);
while(!queue1.isEmpty())
{
queue2.add(queue1.poll());
}
Queue<Integer> temp = queue1;
queue1 = queue2;
queue2 = temp;
}
/** Removes the element on top of the stack and returns that element. */
public int pop() {
return queue1.poll();
}
/** Get the top element. */
public int top() {
return queue1.peek();
}
/** Returns whether the stack is empty. */
public boolean empty() {
return queue1.isEmpty();
}
}
/**
* Your MyStack object will be instantiated and called as such:
* MyStack obj = new MyStack();
* obj.push(x);
* int param_2 = obj.pop();
* int param_3 = obj.top();
* boolean param_4 = obj.empty();
*/