134 lines
2.6 KiB
C++
134 lines
2.6 KiB
C++
/* Problem URL: https://codeforces.com/problemset/problem/919/D */
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#include <bits/stdc++.h>
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using namespace std;
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#define V vector
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#define rmin(a, b) a = min(a, b)
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#define rmax(a, b) a = max(a, b)
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#define rep(i, lim) for (size_t i = 0; i < (lim); i++)
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#define nrep(i, s, lim) for (size_t i = s; i < (lim); i++)
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#define repv(i, v) for (auto &i : (v))
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#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
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#define sortv(v) sort(v.begin(), v.end())
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#define all(v) (v).begin(), (v).end()
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using vi = vector<int>;
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using vvi = vector<vi>;
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using vvvi = vector<vvi>;
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using vvvvi = vector<vvvi>;
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using ll = long long;
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using vl = vector<ll>;
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using vvl = vector<vl>;
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using vvvl = vector<vvl>;
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using vvvvl = vector<vvvl>;
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template<class v>
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auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
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os << vec[0];
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for (size_t i = 1; i < vec.size(); i++) {
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os << ' ' << vec[i];
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}
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os << '\n';
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return os;
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}
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template<class v>
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auto operator>>(istream &is, vector<v> &vec)->istream& {
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for (auto &i : vec) {
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is >> i;
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}
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return is;
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}
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template<class v>
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auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
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for (auto &i : vec) {
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os << i[0];
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for (size_t j = 1; j < i.size(); j++) {
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os << ' ' << i[j];
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}
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os << '\n';
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}
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return os;
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}
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template<class v>
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auto operator>>(istream &is, vector<vector<v>> &vec)->istream& {
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for (auto &i : vec) {
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for (auto &j : i) {
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is >> j;
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}
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}
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return is;
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}
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int main()
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{
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ios::sync_with_stdio(false);
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cin.tie(nullptr);
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int n, m;
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cin >> n >> m;
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string a;
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cin >> a;
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vvi graph(n);
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while (m--) {
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int u, v;
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cin >> u >> v;
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u--, v--;
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graph[u].push_back(v);
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}
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vvi dp(n, vi(26, 0));
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V<bool> vis(n, false);
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V<bool> current(n, false);
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function<bool(int i)> dfs = [&](int i){
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vis[i] = true;
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current[i] = true;
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for (auto j : graph[i]) {
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if (current[j]) {
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return true;
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}
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if (!vis[j]) {
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if (dfs(j)) {
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return true;
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}
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}
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rep(k, 26) {
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rmax(dp[i][k], dp[j][k]);
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}
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}
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dp[i][a[i] - 'a']++;
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current[i] = false;
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return false;
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};
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int ans = 0;
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rep(i, n) {
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if (!vis[i]) {
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if (dfs(i)) {
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cout << "-1\n";
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return 0;
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}
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rmax(ans, *max_element(all(dp[i])));
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}
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}
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cout << ans << '\n';
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}
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