思路:
用两个栈实现队列的功能。
c++ code:
class Queue {
public:
stack<int> s, tmp;
// Push element x to the back of queue.
void push(int x) {
s.push(x);
}
// Removes the element from in front of queue.
void pop(void) {
while(s.size() > 1) {
tmp.push(s.top());
s.pop();
}
s.pop();
while(tmp.size() > 0) {
s.push(tmp.top());
tmp.pop();
}
}
// Get the front element.
int peek(void) {
while(s.size() > 1) {
tmp.push(s.top());
s.pop();
}
int v = s.top();
while(tmp.size() > 0) {
s.push(tmp.top());
tmp.pop();
}
return v;
}
// Return whether the queue is empty.
bool empty(void) {
return s.empty();
}
};