代码

#include<cstdio>
#include<cctype>
#include<algorithm>
inline int getint() {
	register char ch;
	while(!isdigit(ch=getchar()));
	register int x=ch^'0';
	while(isdigit(ch=getchar())) x=(((x<<2)+x)<<1)+(ch^'0');
	return x;
}
const int N=301,mod=1e9+7;
int n,a[N],b[N],h[N],ans;
inline int movel(int p) {
	int hs=h[p],ret=0;
	while(--p>=1) {
		if(h[p]>hs) break;
		ret++;
	}
	return ret;
}
inline int mover(int p) {
	int hs=h[p],ret=0;
	while(++p<=n) {
		if(h[p]>=hs) break;
		ret++;
	}
	return ret;
}
inline bool check() {
	for(register int s=1;s<=n;s++) {
		if(std::abs(movel(s)-mover(s))>2) return false;
	}
	return true;
}
void dfs(const int &d) {
	if(d>n) {
		if(check()) (++ans)%=mod;
		return;
	}
	for(h[d]=a[d];h[d]<=b[d];h[d]++) dfs(d+1);
}
int main() {
	n=getint();
	for(register int i=1;i<=n;i++) {
		a[i]=getint();
		b[i]=getint();
	}
	dfs(1);
	printf("%d\n",ans);
	return 0;
}

评测结果