1 files changed, 116 insertions, 0 deletions
diff --git a/2020/February/help.cpp b/2020/February/help.cpp
new file mode 100644
index 0000000..e6ae965
--- /dev/null
+++ b/2020/February/help.cpp
@@ -0,0 +1,116 @@
+#include <bits/stdc++.h>
+#include <ext/pb_ds/tree_policy.hpp>
+#include <ext/pb_ds/assoc_container.hpp>
+#include <ext/rope>
+#define init_io(s) ifstream cin((string)s+".in"); ofstream cout((string)s+".out"); ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL)
+#define FOR(i, a, b, in) for (int i = (a); i < (b); i += in)
+#define REP(i, a, b) for (int i = (a); i < (b); i++)
+#define RFOR(i, a, b, in) for (int i = (a) - 1; i >= (b); i -= in)
+#define RREP(i, a, b) for (int i = (a) - 1; i >= (b); i--)
+#define trav(a, x) for (auto& a : x)
+#define mp make_pair
+#define pb push_back
+#define eb emplace_back
+#define f first
+#define s second
+#define lb lower_bound
+#define ub upper_bound
+#define sz(x) (int)x.size()
+#define all(x) begin(x), end(x)
+#define rsz resize
+#define mem(a, b) memset(a, (b), sizeof(a))
+using namespace std;
+using namespace __gnu_pbds;
+using namespace __gnu_cxx;
+typedef string str;
+typedef long long ll;
+typedef long double ld;
+typedef complex<ld> cd;
+typedef pair<int, int> ii; typedef pair<ll, ll> pl; typedef pair<ld, ld> pd;
+typedef vector<int> vi; typedef vector<ll> vl; typedef vector<ld> vd;
+typedef vector<ii> vii; typedef vector<pl> vpl; typedef vector<pd> vpd;
+typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
+typedef tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_multiset; // WARNING: May be broken
+constexpr int INF = 1e9;
+constexpr ll LINF = 1e18;
+constexpr ll MOD = 1e9+7;
+const ld PI = 4*atan((ld)1);
+
+inline int imod(int i) { return i > MOD ? i - MOD : i; }
+
+int N, pow2[100005] = { 1 };
+ii S[100005];
+struct seg_tree {
+	int seg[800005] = { 0 }, tmp[800005] = { 0 };
+	void pull(int n) { seg[n] = imod(seg[n<<1]+seg[n<<1|1]); }
+	void push(int l, int r, int n) {
+		seg[n] = ((ll)pow2[tmp[n]]*seg[n])%MOD;
+		if (l != r) tmp[n<<1] += tmp[n], tmp[n<<1|1] += tmp[n];
+		tmp[n] = 0;
+	}
+	void update(int x, int v, int l = 1, int r = -1, int n = 1) {
+		if (r == -1) r = 2*N;
+		if (tmp[n]) push(l, r, n);
+		if (l == r) seg[n] = imod(v+seg[n]);
+		else {
+			int m = (l + r) >> 1;
+			x <= m ? update(x, v, l, m, n<<1) : update(x, v, m + 1, r, n<<1|1);
+			pull(n);
+		}
+	}
+	void update_range(int a, int b, int l = 1, int r = -1, int n = 1) {
+		if (r == -1) r = 2*N;
+		if (tmp[n]) push(l, r, n);
+		if (l > b || r < a) return;
+		if (l >= a && r <= b) {
+			tmp[n]++;
+			push(l, r, n);
+		}
+		else {
+			int m = (l + r) >> 1;
+			update_range(a, b, l, m, n<<1), update_range(a, b, m + 1, r, n<<1|1);
+			pull(n);
+		}
+	}
+	int query(int a, int b, int l = 1, int r = -1, int n = 1) {
+		if (r == -1) r = 2*N;
+		if (a > b || l > b || r < a) return 0;
+		if (tmp[n]) push(l, r, n);
+		if (l >= a && r <= b) return seg[n];
+		int m = (l + r) >> 1;
+		return imod(query(a, b, l, m, n<<1) + query(a, b, m + 1, r, n<<1|1));
+	}
+} dp[11];
+
+int main() {
+	init_io("help");
+
+	int fact[11] = { 1 }, nCr[11][11];
+	for (int i = 0; i < 10; i++) fact[i+1] = (i+1)*fact[i];
+	for (int i = 0; i <= 10; i++) {
+		for (int j = 0; j <= i; j++) nCr[i][j] = fact[i]/fact[j]/fact[i-j];
+	}
+	for (int i = 0; i < 100000; i++) pow2[i+1] = imod(pow2[i]<<1);
+
+	int K;
+	cin >> N >> K;
+	for (int i = 0; i < N; ++i) cin >> S[i].f >> S[i].s;
+	sort(S, S + N);
+
+	for (int i = 0; i < N; ++i) {
+		int tmp[11];
+		for (int j = 0; j <= K; ++j) {
+			tmp[j] = dp[j].query(1, S[i].f);
+			ll sum = dp[j].query(S[i].f, S[i].s-1);
+			for (int k = 0; k <= j; ++k) {
+				sum += (ll)nCr[j][k]*tmp[k];
+			}
+			dp[j].update(S[i].s, sum%MOD+1);
+		}
+		for (int j = 0; j <= K; ++j) {
+			dp[j].update_range(S[i].s+1, 2*N);
+		}
+	}
+
+	cout << dp[K].query(1, 2*N) << endl;
+}