Maximum number of iterations is ~63245 because $$$(N+1)*N/2<MAX$$$ .

So in total it will be $$$6*(1e8)$$$ which is fine.

Even if was a pure 1e9, it still depends on other constants. There are huge differences between performing 1e9 additions and 1e9 prints, and the former even fits in like 0.5s, whilte the latter can't run even in 10s. Pushing to a vector is a little more heavier, but 6e8 still barely fits in 2s.

It's about luck. You just need to spam hacks with slightly different values every time. Execution time is unstable enough to make 100~200 ms differences with many many tries, while different test cases make barely any effect on it on average (as long as you keep $$$t=10^4$$$).