题目:用2个栈(先进后出)实现队列(先进先出)
分析:用栈1导入栈2就可以了。
代码:
class Queue {
private:
stack<int> s1;
stack<int> s2;
public:
// Push element x to the back of queue.
void push(int x) {
s1.push(x);
}
// Removes the element from in front of queue.
void pop(void) {
if (s2.empty()){
while(!s1.empty()){
int tmp = s1.top();
s1.pop();
s2.push(tmp);
}
}
s2.pop();
}
// Get the front element.
int peek(void) {
if (s2.empty()){
while(!s1.empty()){
int tmp = s1.top();
s1.pop();
s2.push(tmp);
}
}
return s2.top();
}
// Return whether the queue is empty.
bool empty(void) {
return (s1.empty()&& s2.empty());
}
};