Implementing Queue using Stacks
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.
Notes:
- You must use only standard operations of a stack -- which means only
push to top
,peek/pop from top
,size
, andis empty
operations are valid. - Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
- You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).
Analyse: Using two stacks: in & out to store the information. IN stack is used to push element while OUT stack is used to pop out element. If two stacks are both empty, then the queue is empty.
1 class Queue { 2 private: 3 stack<int> in; 4 stack<int> out; 5 void move(){//move all elements in the IN stack to the OUT stack 6 while(!in.empty()){ 7 out.push(in.top()); 8 in.pop(); 9 } 10 } 11 public: 12 // Push element x to the back of queue. 13 void push(int x) { 14 in.push(x); 15 } 16 17 // Removes the element from in front of queue. 18 void pop(void) {//be careful about the condition 19 if(out.empty()) move(); //if the out stack is empty, then move all elements from IN stack to OUT stack 20 if(!out.empty()) out.pop();//if the out stack is not empty, then pop out the top element 21 } 22 23 // Get the front element. 24 int peek(void) { 25 if(out.empty()) move(); 26 if(!out.empty()) return out.top(); 27 } 28 29 // Return whether the queue is empty. 30 bool empty(void) { 31 return in.empty() && out.empty(); 32 } 33 };
【推荐】编程新体验,更懂你的AI,立即体验豆包MarsCode编程助手
【推荐】凌霞软件回馈社区,博客园 & 1Panel & Halo 联合会员上线
【推荐】抖音旗下AI助手豆包,你的智能百科全书,全免费不限次数
【推荐】博客园社区专享云产品让利特惠,阿里云新客6.5折上折
【推荐】轻量又高性能的 SSH 工具 IShell:AI 加持,快人一步