# QUEUE-USING-TWO-STACKS hackerrank Solution - Correct, Optimal and Working

``````/*
*  Author: Arpit Bhayani
*  https://arpitbhayani.me
*/
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <climits>
#include <deque>
#include <iostream>
#include <list>
#include <limits>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <vector>

#define ll long long

#define MIN(a, b) a < b ? a : b
#define MAX(a, b) a > b ? a : b

using namespace std;

int i = 0;
char ch;
while((ch = getchar()) != '\n') {
str[i++] = ch;
}
str[i] = '\0';
return i;
}

stack<int> s1;
stack<int> s2;
int front_val;

void enqueue(int x) {
while(!s2.empty()) {
s1.push(s2.top());
s2.pop();
}
if(s1.empty()) {
front_val = x;
}
s1.push(x);
}

int dequeue() {
while(!s1.empty()) {
s2.push(s1.top());
s1.pop();
}
int x = s2.top();
s2.pop();
if(!s2.empty()) {
front_val = s2.top();
}
return x;
}

int front() {
return front_val;
}

int main(int argc, char *argv[]) {
int t;
scanf("%d", &t);
while(t--) {
int op;
scanf("%d", &op);
switch(op) {
case 1:
int x;
scanf("%d", &x);
enqueue(x);
break;
case 2:
dequeue();
break;
case 3:
printf("%d\n", front());
break;
}

}

return 0;
}
``````