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constexpr char MIN_CHAR = 'a';
constexpr long long ALPHABET_SIZE = 26;
struct SuffixAutomaton {
struct State {
int length, link;
vector<int> next;
State() : next(ALPHABET_SIZE) {}
};
vector<State> states;
int size, last;
SuffixAutomaton(string &s) {
states.resize(2 * sz(s));
size = 1; last = 0;
states[0].length = 0;
states[0].link = -1;
for (auto c : s) extend(c - MIN_CHAR);
}
void extend(int c) {
int current = size++;
states[current].length = states[last].length + 1;
int pos = last;
while (pos != -1 && !states[pos].next[c]) {
states[pos].next[c] = current;
pos = states[pos].link;
}
if (pos == -1) states[current].link = 0;
else {
int q = states[pos].next[c];
if (states[pos].length + 1 == states[q].length) {
states[current].link = q;
} else {
int clone = size++;
states[clone].length = states[pos].length + 1;
states[clone].link = states[q].link;
states[clone].next = states[q].next;
while (pos != -1 && states[pos].next[c] == q) {
states[pos].next[c] = clone;
pos = states[pos].link;
}
states[q].link = states[current].link = clone;
}}
last = current;
}
// Pair with start index and length of LCS.
// Index in parameter t.
pair<int, int> longestCommonSubstring(string &t) {
int v = 0, l = 0, best = 0, bestpos = 0;
for (int i = 0; i < (int)t.size(); i++) {
int c = t[i] - MIN_CHAR;
while (v && !states[v].next[c]) {
v = states[v].link;
l = states[v].length;
}
if (states[v].next[c]) {v = states[v].next[c]; l++;}
if (l > best) {best = l; bestpos = i;}
}
return {bestpos - best + 1, best};
}
// Returns all terminals of the automaton.
vector<int> calculateTerminals() {
vector<int> terminals;
int pos = last;
while (pos != -1) {
terminals.push_back(pos);
pos = states[pos].link;
}
return terminals;
}
};
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