leetcode stack 232. Implement Queue using Stacks

class Queue {
private:
stack<int> q_input;
stack<int> q_output;
public:
// Push element x to the back of queue.
void push(int x) {
q_input.push(x);
}

// Removes the element from in front of queue.
void pop(void) {
while(!q_input.empty())
{
int top_tmp = q_input.top();
q_input.pop();
q_output.push(top_tmp);
}

if(!q_output.empty())
q_output.pop();
while(!q_output.empty())
{
int top_tmp = q_output.top();
q_output.pop();
q_input.push(top_tmp);
}
}

// Get the front element.
int peek(void) {
while(!q_input.empty())
{
int top_tmp = q_input.top();
q_input.pop();
q_output.push(top_tmp);
}

int result = 0;
if(!q_output.empty())
result = q_output.top();

while(!q_output.empty())
{
int top_tmp = q_output.top();
q_output.pop();
q_input.push(top_tmp);
}

return result;
}

// Return whether the queue is empty.
bool empty(void) {
return q_input.empty();
}
};

class Queue {
stack<int> input, output;
public:

void push(int x) {
input.push(x);
}

void pop(void) {
peek();
output.pop();
}

int peek(void) {
if (output.empty())
while (input.size())
output.push(input.top()), input.pop();
return output.top();
}

bool empty(void) {
return input.empty() && output.empty();
}
};

class Queue {
public:
stack<int> s;

// Push element x to the back of queue.
void push(int x) {
pushHelper(x);
}

void pushHelper(int x){
if(s.size()==0){
s.push(x);
return;
}
int data;
data = s.top();
s.pop();
pushHelper(x);
s.push(data);
return;
}

// Removes the element from in front of queue.
void pop(void) {
s.pop();
}

// Get the front element.
int peek(void) {
return s.top();
}

// Return whether the queue is empty.
bool empty(void) {
return (s.size()==0);
}
};