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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).
题目大意:利用队列实现栈的push、pop、top和empty操作。
解题思路:每次进行push操作时,都把该元素放到队首,其他元素按照顺序移至队尾。其他各操作与C++STL中的队列操作基本一致。
代码如下:
class MyStack {
public:
/** Initialize your data structure here. */
MyStack() {
while(que.size()) que.pop();
}
/** Push element x onto stack. */
void push(int x) {
que.push(x);
int sz = que.size();
while(sz > 1) {
que.push(que.front());
que.pop();
sz--;
}
}
/** Removes the element on top of the stack and returns that element. */
int pop() {
int tmp = que.front();
que.pop();
return tmp;
}
/** Get the top element. */
int top() {
return que.front();
}
/** Returns whether the stack is empty. */
bool empty() {
return que.empty();
}
private:
queue<int> que;
};
本文标签: 队列LeetCodeimplementqueuesStack
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