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原题网址:https://leetcode/problems/implement-stack-using-queues/
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).
源代码:
class MyStack {
private Queue<Integer> queue = new LinkedList<Integer>();
private Queue<Integer> buf = new LinkedList<Integer>();
// Push element x onto stack.
public void push(int x) {
buf.add(x);
while (!queue.isEmpty()) buf.add(queue.remove());
Queue<Integer> temp = queue;
queue = buf;
buf = temp;
}
// Removes the element on top of the stack.
public void pop() {
queue.remove();
}
// Get the top element.
public int top() {
return queue.peek();
}
// Return whether the stack is empty.
public boolean empty() {
return queue.isEmpty();
}
}
时间复杂度:压栈O(n),出栈、查看栈顶为O(1),空间复杂度为O(n)
本文标签: 队列来实现LeetCodeimplementqueues
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