Hello Codeforcers! I need your help to debug this strange TLE verdict. I was trying to implement the editorial of the problem [D. Chip Moves](https://codeforces.net/contest/1716/problem/D). My implementation which is very similar to the editorial is this: ↵
↵
↵
```c++↵
using ll = long long;↵
#define rep(i, n) for (ll i=0; i<n; ++i)↵
#define rep1(i, n) for (ll i=1; i<=n; ++i)↵
↵
const ll MAXN = 2e5 + 5;↵
ll A[MAXN][4];↵
↵
void solve() {↵
constexpr ll mod = 998244353;↵
↵
memset(A, 0, sizeof A); ↵
↵
ll n; cin >> n;↵
ll k; cin >> k;↵
↵
ll tot = 0;↵
ll step = k;↵
↵
ll CUR = 0;↵
ll DP = 1;↵
ll SAME = 2;↵
ll ANS = 3;↵
↵
A[0][DP] = 1; ↵
↵
ll iters = 0;↵
while ((tot += step) <= n) {↵
iters++;↵
↵
rep (i, n+1) A[i][CUR] = 0;↵
↵
rep (i, step) A[i][SAME] = 0;↵
↵
for (ll i = max<ll>(step-4, 0); i <= n; ++i) { ↵
(A[i][CUR] += A[i % step][SAME]) %= mod;↵
↵
// This line seems to cause the TLE↵
(A[i][ANS] += A[i][CUR]) %= mod; ↵
↵
(A[i % step][SAME] += A[i][DP]) %= mod;↵
} ↵
↵
swap(CUR, DP);↵
step++;↵
}↵
↵
for (ll i = 1; i <= n; ++i) {↵
cout << A[i][ANS] << " ";↵
}↵
↵
cout << endl;↵
↵
// cerr << "iters: " << iters << endl; ↵
↵
}↵
```↵
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↵
which received a TLE verdict. Upon testing this locally, it seems to work pretty fast uptill n = 170000, but when putting n = 180000, the program suddenly stops running and hangs. Upon further investigation inside the solve function, this one line `(A[i][ANS] += A[i][CUR]) %= mod;` seems to be the issue! Just uncommenting this one line gives the solution extremely fast (although obviously wrong)! However uncommenting this line out causes the program to TLE. ↵
↵
What is about this one small line which is a simple O(1) operation which causes the whole program to simply hang? I've been stuck on this weird bug for a while and would like to seek your help.↵
↵
↵
```c++↵
using ll = long long;↵
#define rep(i, n) for (ll i=0; i<n; ++i)↵
#define rep1(i, n) for (ll i=1; i<=n; ++i)↵
↵
const ll MAXN = 2e5 + 5;↵
ll A[MAXN][4];↵
↵
void solve() {↵
constexpr ll mod = 998244353;↵
↵
memset(A, 0, sizeof A); ↵
↵
ll n; cin >> n;↵
ll k; cin >> k;↵
↵
ll tot = 0;↵
ll step = k;↵
↵
ll CUR = 0;↵
ll DP = 1;↵
ll SAME = 2;↵
ll ANS = 3;↵
↵
A[0][DP] = 1; ↵
↵
ll iters = 0;↵
while ((tot += step) <= n) {↵
iters++;↵
↵
rep (i, n+1) A[i][CUR] = 0;↵
↵
rep (i, step) A[i][SAME] = 0;↵
↵
for (ll i = max<ll>(step-4, 0); i <= n; ++i) { ↵
(A[i][CUR] += A[i % step][SAME]) %= mod;↵
↵
// This line seems to cause the TLE↵
(A[i][ANS] += A[i][CUR]) %= mod; ↵
↵
(A[i % step][SAME] += A[i][DP]) %= mod;↵
} ↵
↵
swap(CUR, DP);↵
step++;↵
}↵
↵
for (ll i = 1; i <= n; ++i) {↵
cout << A[i][ANS] << " ";↵
}↵
↵
cout << endl;↵
↵
// cerr << "iters: " << iters << endl; ↵
↵
}↵
```↵
↵
↵
which received a TLE verdict. Upon testing this locally, it seems to work pretty fast uptill n = 170000, but when putting n = 180000, the program suddenly stops running and hangs. Upon further investigation inside the solve function, this one line `(A[i][ANS] += A[i][CUR]) %= mod;` seems to be the issue! Just uncommenting this one line gives the solution extremely fast (although obviously wrong)! However uncommenting this line out causes the program to TLE. ↵
↵
What is about this one small line which is a simple O(1) operation which causes the whole program to simply hang? I've been stuck on this weird bug for a while and would like to seek your help.↵
