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constexpr int ALPHABET_SIZE = 26;
constexpr char OFFSET = 'a';
struct SuffixAutomaton {
struct State {
int len, link = -1;
array<int, ALPHABET_SIZE> nxt; // map if large Alphabet
State(int l) : len(l) {fill(all(nxt), -1);}
};
vector<State> st = {State(0)};
int cur = 0;
SuffixAutomaton(const string& s) {
st.reserve(2 * sz(s));
for (auto c : s) extend(c - OFFSET);
}
void extend(int c) {
int p = cur;
cur = sz(st);
st.emplace_back(st[p].len + 1);
for (; p != -1 && st[p].nxt[c] < 0; p = st[p].link) {
st[p].nxt[c] = cur;
}
if (p == -1) {
st[cur].link = 0;
} else {
int q = st[p].nxt[c];
if (st[p].len + 1 == st[q].len) {
st[cur].link = q;
} else {
st.emplace_back(st[p].len + 1);
st.back().link = st[q].link;
st.back().nxt = st[q].nxt;
for (; p != -1 && st[p].nxt[c] == q; p = st[p].link) {
st[p].nxt[c] = sz(st) - 1;
}
st[q].link = st[cur].link = sz(st) - 1;
}}}
vector<int> calculateTerminals() {
vector<int> terminals;
for (int p = cur; p != -1; p = st[p].link) {
terminals.push_back(p);
}
return terminals;
}
// Pair with start index (in t) and length of LCS.
pair<int, int> longestCommonSubstring(const string& t) {
int v = 0, l = 0, best = 0, bestp = -1;
for (int i = 0; i < sz(t); i++) {
int c = t[i] - OFFSET;
while (v > 0 && st[v].nxt[c] < 0) {
v = st[v].link;
l = st[v].len;
}
if (st[v].nxt[c] >= 0) v = st[v].nxt[c], l++;
if (l > best) best = l, bestp = i;
}
return {bestp - best + 1, best};
}
};
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