leetcode_232——Implement Queue using Stacks（栈与队列）

Implement Queue using Stacks

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Question  Solution 

 

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).

 

 

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#include<iostream>

#include<stack>

using namespace std;





stack<int> sta1;

stack<int> sta2;



// Push element x to the back of queue.

void push(int x) {

	sta1.push(x);

}



// Removes the element from in front of queue.

void pop(void) {

	while(!sta1.empty())

	{

		sta2.push(sta1.top());

		sta1.pop();

	}

	sta2.pop();

	while(!sta2.empty())

	{

		sta1.push(sta2.top());

		sta2.pop();

	}

}



// Get the front element.

int peek(void) {

	while(!sta1.empty())

	{

		sta2.push(sta1.top());

		sta1.pop();

	}

	int a=sta2.top();

	while(!sta2.empty())

	{

		sta1.push(sta2.top());

		sta2.pop();

	}

	return a;

}



// Return whether the queue is empty.

bool empty(void) {

	if(sta1.empty())

		return 1;

	else

		return 0;

}



int main()

{

	

}