Implement 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).
两个栈实现堆是经典算法。
进队时,压入stk1。
出队时,stk2弹出。
stk2为空时,stk1倒入stk2。两次逆序恢复了原序。
class Queue { public: stack<int> stk1; // push stack<int> stk2; // pop // Push element x to the back of queue. void push(int x) { stk1.push(x); } // Removes the element from in front of queue. void pop(void) { if(stk2.empty()) { while(!stk1.empty()) { int top = stk1.top(); stk1.pop(); stk2.push(top); } } stk2.pop(); } // Get the front element. int peek(void) { if(stk2.empty()) { while(!stk1.empty()) { int top = stk1.top(); stk1.pop(); stk2.push(top); } } return stk2.top(); } // Return whether the queue is empty. bool empty(void) { return stk1.empty()&&stk2.empty(); } };
时间: 2024-10-11 04:02:18