Google KickStart Round B Bus Routes Problem wrong answer? - c++

Question

I was practicing with google kickstart's round B bus route problem. I actually looked at their analysis and implemented their alternative answer.
I'll also paste the problem prompt below my code.
https://codingcompetitions.withgoogle.com/kickstart/round/000000000019ffc8/00000000002d83bf
And my solution passes the first test set but gets a wrong answer on the second test set. I have no idea what the second test set is, only that it's very big. I'm pretty confused as my solution follows the analysis of the problem, and is actually an implementation of the alternate provided solution to a T. I also have no idea how to figure out which test case could be giving a wrong answer, there seems to be so many possibilities!
I have no idea how to even debug such a vague answer. Maybe there are some edge cases I'm not considering?
#include <iostream> // includes cin to read from stdin and cout to write to stdout
#include <bits/stdc++.h>
using namespace std;
int main() {
int t, n, d;
cin >> t; // read t. cin knows that t is an int, so it reads it as such.
for (int i = 1; i <= t; ++i) {
cin >> n >> d; // read n and then m.
stack <int> bus;
for(int j=0; j<n; j++){
int x;
cin >> x;
bus.push(x);
}
while(!bus.empty()){
int b = bus.top();
bus.pop();
d = d - d%b;
}
cout << "Case #" << i << ": " << d << endl;
}
return 0;
}
****Here's a shortened version of the Problem Prompt ****
Problem
Bucket is planning to make a very long journey across the countryside by bus. Her journey consists of N bus routes, numbered from 1 to N in the order she must take them. The buses themselves are very fast, but do not run often. The i-th bus route only runs every Xi days.
More specifically, she can only take the i-th bus on day Xi, 2Xi, 3Xi and so on. Since the buses are very fast, she can take multiple buses on the same day.
Bucket must finish her journey by day D, but she would like to start the journey as late as possible. What is the latest day she could take the first bus, and still finish her journey by day D?
It is guaranteed that it is possible for Bucket to finish her journey by day D.
Input
The first line of the input gives the number of test cases, T. T test cases follow. Each test case begins with a line containing the two integers N and D. Then, another line follows containing N integers, the i-th one is Xi.
Output
For each test case, output one line containing Case #x: y, where x is the test case number (starting from 1) and y is the latest day she could take the first bus, and still finish her journey by day D.
Limits
Time limit: 10 seconds per test set.
Memory limit: 1GB.

Answer 1

my guess is using int is not sufficient as D can be up to 10^12 in test set 2
Edited: I verified my guess. You will be able to solve the problem by fixing this bug. And I believe the use of long long is common for coding contests, i.e. take note of the input/output constraints every time.

Answer 2

#include <iostream>
#include <bits/stdc++.h>
using namespace std;
int main ()
{
int t;
long long int x,i,j,n,d;
cin >> t;
for ( i = 0; i < t; i++)
{
cin >> n >> d;
stack < long long int >route;
for (j = 0; j < n; j++)
{
cin >> x;
route.push (x);
}
while (!route.empty ())
{
long long int c = route.top ();
route.pop ();
d = d - d % c;
}
cout << "Case #" << i+1 << ": " << d << endl;
}
return 0;
}