1.描述
Implement the following operations of a queue using stacks.
push(x) -- Push element x to the back of queue.
pop() -- Removes the element from in front of queue.
peek() -- Get the front element.
empty() -- Return whether the queue is empty.
2.分析
3.代码
class MyQueue {
public:
/** Initialize your data structure here. */
MyQueue() {
}
/** Push element x to the back of queue. */
void push(int x) {
while (!s2.empty()) {
s1.push(s2.top());
s2.pop();
}
s1.push(x);
}
/** Removes the element from in front of queue and returns that element. */
int pop() {
if (empty()) exit(-1);
while (!s1.empty()) {
s2.push(s1.top());
s1.pop();
}
int ans = s2.top();
s2.pop();
return ans;
}
/** Get the front element. */
int peek() {
if (empty()) exit(-1);
while (!s1.empty()) {
s2.push(s1.top());
s1.pop();
}
return s2.top();
}
/** Returns whether the queue is empty. */
bool empty() {
return s1.empty() && s2.empty();
}
private:
stack<int> s1, s2;
};
/**
* 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();
* bool param_4 = obj.empty();
*/
