LeetCode-Implement Queue using Stacks

標籤：

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, and is 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).

class MyQueue {    Stack<Integer> inStack=new Stack<Integer>();    Stack<Integer> outStack=new Stack<Integer>();    // Push element x to the back of queue.    public void push(int x) {        inStack.push(x);    }    // Removes the element from in front of queue.    public void pop() {                if(!outStack.empty()){            outStack.pop();        }                else{            while(!inStack.empty()){                int value=inStack.pop();                outStack.push(value);            }            outStack.pop();        }            }    // Get the front element.    public int peek() {        int res=0;        if(!outStack.empty()){            res=outStack.peek();        }        else{            while(!inStack.empty()){                int value=inStack.pop();                outStack.push(value);            }            res=outStack.peek();        }        return res;    }    // Return whether the queue is empty.    public boolean empty() {        if(inStack.empty() && outStack.empty()){            return true;        }        return false;    }}

 

LeetCode-Implement Queue using Stacks