170 lines
3.3 KiB
C++
170 lines
3.3 KiB
C++
/* Problem URL: https://codeforces.com/contest/2152/problem/C */
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#include <bits/stdc++.h>
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#include <ext/pb_ds/assoc_container.hpp>
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#include <ext/pb_ds/tree_policy.hpp>
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using namespace std;
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using namespace __gnu_pbds;
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template <class T, class comp = less<>>
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using ordered_set = tree<T, null_type , comp , rb_tree_tag , tree_order_statistics_node_update>;
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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 (int i = 0; i < (lim); i++)
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#define nrep(i, s, lim) for (int 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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const int oo = INT32_MAX >> 1;
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const ll OO = INT64_MAX >> 1;
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void pre()
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{
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}
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#define TEST 1
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void solve()
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{
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int n, q;
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cin >> n >> q;
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vi a(n);
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cin >> a;
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if (n == 1) {
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while (q--) {
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int a, b;
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cin >> a >> b;
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cout << "-1\n";
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}
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return;
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}
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V<bool> val(n);
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nrep(i, 1, n - 1) {
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if (a[i] != a[i - 1] && a[i] != a[i + 1]) {
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val[i] = true;
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}
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}
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if (a[0] != a[1]) {
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val[0] = true;
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}
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if (a[n - 1] != a[n - 2]) {
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val[n - 1] = true;
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}
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vi count(n + 1);
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rep(i, n) {
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count[i + 1] = count[i] + a[i];
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}
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vvi sparse(20, vi(n));
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rep(i, n) {
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sparse[0][i] = val[i];
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}
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nrep(j, 1, 20) {
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for (int i = 0; i + (1 << (j - 1)) < n; i++) {
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sparse[j][i] = sparse[j - 1][i] && sparse[j - 1][i + (1 << (j - 1))];
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}
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}
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auto query = [&](int l, int r) {
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int log = 31 - __builtin_clz(r - l + 1);
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return sparse[log][l] & sparse[log][r - (1 << log) + 1];
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};
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while (q--) {
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int l, r;
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cin >> l >> r;
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l--, r--;
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if ((r - l + 1) % 3 || (count[r + 1] - count[l]) % 3) {
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cout << "-1\n";
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continue;
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}
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cout << (r - l + 1) / 3 + (query(l + 1, r - 1) & (a[l] != a[l + 1]) & (a[r] != a[r - 1])) << '\n';
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}
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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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pre();
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int t;
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(TEST && cin >> t) || (t = 1);
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while (t--) {
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solve();
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}
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}
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