Codeforces 874div3 F
// compile: make data
// run: ./data < data.in
#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#ifdef LOCAL
#include <debug/codeforces.h>
#define debug(x...) _debug_print(#x, x);
#else
#define debug(x...) {};
#endif
template<typename...Args> void print_(Args...args){((cout<<args<<" "),...)<<endl;}
#define rep(i,a,b) for(int i=(a);i<(int)(b);++i)
#define sz(v) ((int)(v).size())
#define print(...) print_(__VA_ARGS__);
#define INTMAX (int)(9223372036854775807)
#define INF (int)(1152921504606846976)
#define double long double
#define int long long
#define MAXN 200010
#define P 1000000007
constexpr long long safe_mod(long long x, long long m) {
x %= m;
if (x < 0) x += m;
return x;
}
constexpr std::pair<long long, long long> inv_gcd(long long a, long long b) {
a = safe_mod(a, b);
if (a == 0) return {b, 0};
long long s = b, t = a;
long long m0 = 0, m1 = 1;
while (t) {
long long u = s / t;
s -= t * u;
m0 -= m1 * u;
auto tmp = s;
s = t;
t = tmp;
tmp = m0;
m0 = m1;
m1 = tmp;
}
if (m0 < 0) m0 += b / s;
return {s, m0};
}
long long inv_mod(long long x, long long m) {
assert(1 <= m);
auto z = inv_gcd(x, m);
assert(z.first == 1);
return z.second;
}
void solve() {
int n, m; cin >> n >> m;
vector<int> a(n);
vector<pair<int, int>> f;
rep(i, 0, n) cin >> a[i];
sort(a.begin(), a.end());
f.push_back({a[0], 1});
rep(i, 1, n) {
if (a[i] == a[i-1]) ++f.back().second;
else f.push_back({a[i], 1});
}
n = sz(f);
int ans = 0;
auto calc = [&](int l, int r) {
int sum = 0;
int mux = 1;
rep(i, l, l+m) mux = (mux * f[i].second) % P;
sum += mux;
for (int i = l+1; i+m-1 <= r; ++i) {
mux = (mux * f[i+m-1].second) % P;
mux = (mux * inv_mod(f[i-1].second, P)) % P;
sum = (sum + mux) % P;
}
return sum;
};
int l = 0, r = 0;
while (l < n) {
while (r+1 < n && f[r+1].first == f[r].first+1) ++r;
if (r-l+1 < m) {
l = ++r;
continue;
}
ans = (ans + calc(l, r)) % P;
l = ++r;
}
cout << ans << endl;
}
int32_t main() {
ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
int _; cin >> _;
while (_--) solve();
return 0;
}
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Source: github.com/k4yt3x/flowerhd
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