admin管理员组文章数量:1636909
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.
- You must use only standard operations of a queue -- which means only
push to back
,peek/pop from front
,size
, andis 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.
思路分析:这题和LeetCode Implement Queue using Stacks类似,思路也类似,用两个队列来模拟一个栈。具体做法是,入栈只需要放入Q1队列尾部。出栈时,把Q1除了最后一个元素之外的所有元素出队列,并且压入Q2队列尾部,然后从Q1中取出最后那个元素。注意要保证Q2为空,它是一个辅助队列,所以我们交换Q1和Q2。top和pop方法类似,除了取出Q1中最后那个元素后,再返回它前还要压入到Q2中去,保证这个元素不被丢失,因为我们只想看栈顶元素,并不想真正将它出栈。
AC Code
class MyStack {
//Queue
LinkedList<Integer> q1 = new LinkedList<Integer>();
LinkedList<Integer> q2 = new LinkedList<Integer>();
// Push element x onto stack.
public void push(int x) {
q1.add(x);
}
// Removes the element on top of the stack.
public void pop() {
//peek(); poll();
while(q1.size() > 1){
q2.add(q1.poll());
}
q1.poll();
//switch
LinkedList<Integer> tem = q1;
q1 = q2;
q2 = tem;
}
// Get the top element.
public int top() {
//peek(); poll();
while(q1.size() > 1){
q2.add(q1.poll());
}
int res = q1.peek();
q2.add(q1.poll());
//switch
LinkedList<Integer> tem = q1;
q1 = q2;
q2 = tem;
return res;
}
// Return whether the stack is empty.
public boolean empty() {
return q1.isEmpty();
}
}
本文标签: implementLeetCodequeuesStack
版权声明:本文标题:LeetCode Implement Stack using Queues 内容由热心网友自发贡献,该文观点仅代表作者本人, 转载请联系作者并注明出处:https://m.elefans.com/xitong/1729234626a1191854.html, 本站仅提供信息存储空间服务,不拥有所有权,不承担相关法律责任。如发现本站有涉嫌抄袭侵权/违法违规的内容,一经查实,本站将立刻删除。
发表评论