#pragma comment(linker, "/STACK:1024000000,1024000000") #include<cstdio> #include<cstring> #include<cmath> #include<algorithm> #include<vector> #include<map> #include<set> #include<queue> #include<stack> #include<iostream> using namespace std; typedef long long LL; const double pi=acos(-1.0),eps=1e-6; void File() { freopen("D:\\in.txt","r",stdin); freopen("D:\\out.txt","w",stdout); } template <class T> inline void read(T &x) { char c=getchar(); x=0; while(!isdigit(c)) c=getchar(); while(isdigit(c)) {x=x*10+c-‘0‘; c=getchar();} } LL mod=1e9+7; const int maxn=1200010; int n,k; LL f[maxn],a[maxn]; struct X { int L,R; }s[maxn]; int c[maxn],b[maxn],sz; LL ans[maxn]; int lowbit(int x){return x&(-x);} int sum(int x) { int res=0; while(x>0) res=res+c[x],x=x-lowbit(x); return res; } void update(int x,int v) { while(x<=1200000) c[x]=c[x]+v,x=x+lowbit(x); } LL extend_gcd(LL a,LL b,LL &x,LL &y) { if(a==0&&b==0) return -1; if(b==0){x=1;y=0;return a;} LL d=extend_gcd(b,a%b,y,x); y-=a/b*x; return d; } LL mod_reverse(LL a,LL n) { LL x,y; LL d=extend_gcd(a,n,x,y); if(d==1) return (x%n+n)%n; else return -1; } int get(int x) { int L=0,R=sz-1,pos=0; while(L<=R) { int mid=(L+R)/2; if(b[mid]<x) L=mid+1; else if(b[mid]==x) pos=mid,R=mid-1; else R=mid-1; } return pos+1; } bool cmp(X a,X b) { return a.L<b.L; } int main() { scanf("%d%d",&n,&k); f[0]=1; for(int i=1;i<=400000;i++) f[i]=i*f[i-1]%mod; for(int i=k;i<=400000;i++) { LL fz=f[i]%mod,fm=f[k]*f[i-k]%mod; LL ni=mod_reverse(fm,mod); a[i]=fz*ni%mod; } for(int i=1;i<=n;i++) { scanf("%d%d",&s[i].L,&s[i].R); b[sz++]=s[i].L, b[sz++]=s[i].R; b[sz++]=s[i].L-1; b[sz++]=s[i].L+1; b[sz++]=s[i].R-1; b[sz++]=s[i].R+1; } sort(b,b+sz); sort(s+1,s+1+n,cmp); int h=1; for(int i=1;i<=sz;i++) { while(h<=n&&get(s[h].L)==i) { update(get(s[h].R),1); h++; } ans[i]=a[sum(1200000)-sum(i-1)]; } LL Ans=0; for(int i=0;i<sz;) { int pos=-1; for(int j=i;j<sz;j++) { if(b[j]>b[i]) { pos=j; break; } } if(pos==-1) { Ans=(Ans+ans[i+1])%mod; break; } Ans=(Ans+(b[pos]-b[i])*ans[i+1]%mod)%mod; i=pos; } printf("%lld\n",Ans); return 0; }
时间: 2024-10-18 16:18:45