代码

#include <bits/stdc++.h>
#define N 25
#define getchar nc
using namespace std;
inline char nc(){
    static char buf[100000],*p1=buf,*p2=buf;
    return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++;
}
inline int read()
{
    register int x=0,f=1;register char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9')x=(x<<3)+(x<<1)+ch-'0',ch=getchar();
    return x*f;
}
inline void write(register int x)
{
    if(!x)putchar('0');if(x<0)x=-x,putchar('-');
    static int sta[20];register int tot=0;
    while(x)sta[tot++]=x%10,x/=10;
    while(tot)putchar(sta[--tot]+48);
}
int n,a[N],b[N];
int v[N];
inline int check()
{
	for(register int i=1;i<=n;++i)
	{
		int l=0,r=0;
		for(register int j=i-1;j>=1;--j)
		{
			if(v[j]>v[i])
				break;
			++l;
		}
		for(register int j=i+1;j<=n;++j)
		{
			if(v[j]>=v[i])
				break;
			++r;
		}
		//printf("%d %d\n",l,r);
		if(fabs(r-l)>2)
			return 0;
	}
	return 1;
}
inline int dfs(register int dep)
{
	int res=0;
	if(dep==n+1)
		return check();
	for(register int i=a[dep];i<=b[dep];++i)
		v[dep]=i,res+=dfs(dep+1);
	return res;
}
int main()
{

	n=read();
	for(register int i=1;i<=n;++i)
		a[i]=read(),b[i]=read();
	write(dfs(1));
	return 0;
}

评测结果