一、题目描述
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.
- 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)
栈和队列
三、CODE描述
栈和队列
import java.util.Stack;
class MyQueue {
// Push element x to the back of queue.
Stack<Integer> stack1 =new Stack<Integer>(); // push
Stack<Integer> stack2 =new Stack<Integer>(); // pop
public void push(int x) {
stack1.push(x);
}
// Removes the element from in front of queue.
public void pop() {
if(stack2.empty()){
while(!stack1.empty()){
int top = stack1.peek();
stack1.pop();
stack2.push(top);
}
}
if(!stack2.empty()){
stack2.pop();
}
}
// Get the front element.
public int peek() {
if(stack2.empty()){
while(!stack1.empty()){
int top = stack1.peek();
stack1.pop();
stack2.push(top);
}
}
if(stack2.empty()) return -1;
else
return stack2.peek();
}
// Return whether the queue is empty.
public boolean empty() {
return stack1.empty()&&stack2.empty();
}
}
四、结果
越努力,越幸运。