代码

/*
Author: QAQ Automaton
Lang: C++
Prog: robot.cpp
Mail: lk@qaq-am.com
Blog: https://www.qaq-am.com/
*/
#include<bits/stdc++.h>
#define int long long 
#define debug(...) fprintf(stderr,__VA_ARGS__)
#define DEBUG printf("Passing [%s] in LINE %d\n",__FUNCTION__,__LINE__)
#define Debug debug("Passing [%s] in LINE %d\n",__FUNCTION__,__LINE__)
#define all(x) x.begin(),x.end()
#define x first
#define y second
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
#define inf 0x3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f
const double eps=1e-8;
const double pi=acos(-1.0);
template<class T>int chkmin(T &a,T b){return a>b?a=b,1:0;}
template<class T>int chkmax(T &a,T b){return a<b?a=b,1:0;}
template<class T>T sqr(T a){return a*a;}
template<class T>T mmin(T a,T b){return a<b?a:b;}
template<class T>T mmax(T a,T b){return a>b?a:b;}
template<class T>T aabs(T a){return a<0?-a:a;}
template<class T>int dcmp(T a,T b){return a>b;}
template<int *a>int cmp_a(int x,int y){return a[x]<a[y];}
#define min mmin
#define max mmax
#define abs aabs
namespace io {
	const int SIZE = (1 << 21) + 1;
	char ibuf[SIZE], *iS, *iT, obuf[SIZE], *oS = obuf, *oT = oS + SIZE - 1, c, qu[55]; int f, qr;
	// getchar
	#define gc() (iS == iT ? (iT = (iS = ibuf) + fread (ibuf, 1, SIZE, stdin), (iS == iT ? EOF : *iS ++)) : *iS ++)
	// print the remaining part
	inline void flush () {
		fwrite (obuf, 1, oS - obuf, stdout);
		oS = obuf;
	}
	// putchar
	inline void putc (char x) {
		*oS ++ = x;
		if (oS == oT) flush ();
	}
	// input a signed integer
	inline bool read (signed &x) {
		for (f = 1, c = gc(); c < '0' || c > '9'; c = gc()) if (c == '-') f = -1;else if(c==EOF)return 0;
		for (x = 0; c <= '9' && c >= '0'; c = gc()) x = x * 10 + (c & 15); x *= f;
		return 1;
	}

	inline bool read (long long &x) {
		for (f = 1, c = gc(); c < '0' || c > '9'; c = gc()) if (c == '-') f = -1;else if(c==EOF)return 0;
		for (x = 0; c <= '9' && c >= '0'; c = gc()) x = x * 10 + (c & 15); x *= f;
		return 1;
	}
	inline bool read (char &x) {
		x=gc();
		return x!=EOF;
	}
	inline bool read(char *x){
		while((*x=gc())=='\n' || *x==' '||*x=='\r')if(*x==EOF)return 0;
		while(!(*x=='\n'||*x==' '||*x=='\r'))*(++x)=gc();
		*x=0;
		return 1;
	}
	template<typename A,typename ...B>
	inline bool read(A &x,B &...y){
		return read(x)&&read(y...);
	}
	// print a signed integer
	inline bool write (signed x) {
		if (!x) putc ('0'); if (x < 0) putc ('-'), x = -x;
		while (x) qu[++ qr] = x % 10 + '0',  x /= 10;
		while (qr) putc (qu[qr --]);
		return 0;
	}

	inline bool write (long long x) {
		if (!x) putc ('0'); if (x < 0) putc ('-'), x = -x;
		while (x) qu[++ qr] = x % 10 + '0',  x /= 10;
		while (qr) putc (qu[qr --]);
		return 0;
	}
	inline bool write (char x) {
		putc(x);
		return 0;
	}
	inline bool write(const char *x){
		while(*x){putc(*x);++x;}
		return 0;
	}
	inline bool write(char *x){
		while(*x){putc(*x);++x;}
		return 0;
	}
	template<typename A,typename ...B>
	inline bool write(A x,B ...y){
		return write(x)||write(y...);
	}
	//no need to call flush at the end manually!
	struct Flusher_ {~Flusher_(){flush();}}io_flusher_;
}
using io :: read;
using io :: putc;
using io :: write;
int f[55][55][105],vis[55][55][105];
int a[55],b[55],ok;
int c[55][55],xc[55],inv[55];
const int p=1000000007;
int dfs(int l,int r,int w){
	if(l>r)return 1;
	if(!w)return 0;
	if(vis[l][r][w])return f[l][r][w];
	vis[l][r][w]=1;
	f[l][r][w]=dfs(l,r,w-1);
	if((l&1) == (r&1)){
		int mid=(l+r)>>1;
		if(a[mid]<=w && w<=b[mid])f[l][r][w]+=dfs(l,mid-1,w)*dfs(mid+1,r,w-1);
		if(mid>l && a[mid-1]<=w && w<=b[mid-1])f[l][r][w]+=dfs(l,mid-2,w)*dfs(mid,r,w-1);
		if(mid<r && a[mid+1]<=w && w<=b[mid+1])f[l][r][w]+=dfs(l,mid,w)*dfs(mid+2,r,w-1);
	}
	else{
		int mid=(l+r)>>1;
		if(a[mid]<=w && w<=b[mid])f[l][r][w]+=dfs(l,mid-1,w)*dfs(mid+1,r,w-1);
		if(mid<r && a[mid+1]<=w && w<=b[mid+1])f[l][r][w]+=dfs(l,mid,w)*dfs(mid+2,r,w-1);
	}
	return f[l][r][w]%=p;
}

signed main(){
	int n;
	read(n);
	ok=1;
	for(int i=1;i<=n;++i){
		read(a[i],b[i]);
		if(b[i]>100)ok=0;
	}
	if(ok){
		write(dfs(1,n,100),'\n');		
	}
	else{
		dfs(1,n,n);
		for(int i=0;i<=n;++i){
			c[i][0]=c[i][i]=1;
			for(int j=1;j<i;++j)c[i][j]=(c[i-1][j]+c[i-1][j-1])%p;
		}
		xc[0]=1;
		inv[0]=1;
		inv[1]=1;
		for(int i=2;i<=n;++i)inv[i]=(p-p/i)*inv[p%i]%p;
		for(int i=1;i<=n;++i)xc[i]=xc[i-1]*(1000000001-i)%p*inv[i]%p;
		int ans=0;
		for(int i=1;i<=n;++i){
			f[1][n][i]=(f[1][n][i]%p+p)%p;
			ans=(ans+xc[i]*f[1][n][i])%p;
			for(int j=i+1;j<=n;++j)f[1][n][j]-=c[j][i]*f[1][n][i]%p;
		}
		write(ans,'\n');
	}
		
	return 0;
}

评测结果