【HDOJ6630】permutation 2（递推）

题意：给定x，y，n，有标号从1到n的n个数组，求合法的排列个数模998244353使得

1：p[1]=x

2：p[n]=y

3：相邻两项的差的绝对值<=2

n<=1e5

思路：

 #include<bits/stdc++.h>
 using namespace std;
 typedef long long ll;
 typedef unsigned int uint;
 typedef unsigned long long ull;
 typedef pair<int,int> PII;
 typedef pair<ll,ll> Pll;
 typedef vector<int> VI;
 typedef vector<PII> VII;
 #define N  1100000
 #define M  4100000
 #define fi first
 #define se second
 #define MP make_pair
 #define pi acos(-1)
 #define mem(a,b) memset(a,b,sizeof(a))
 #define rep(i,a,b) for(int i=(int)a;i<=(int)b;i++)
 #define per(i,a,b) for(int i=(int)a;i>=(int)b;i--)
 #define lowbit(x) x&(-x)
 #define Rand (rand()*(1<<16)+rand())
 #define id(x) ((x)<=B?(x):m-n/(x)+1)
 #define ls p<<1
 #define rs p<<1|1

 const ll MOD=,inv2=(MOD+)/;
       double eps=1e-;
       int INF=1e9;

 int f[];

 int read()
 {
    int v=,f=;
    char c=getchar();
    while(c<||<c) {if(c=='-') f=-; c=getchar();}
    while(<=c&&c<=) v=(v<<)+v+v+c-,c=getchar();
    return v*f;
 }

 int main()
 {
     int cas=read();
     f[]=f[]=f[]=;
     rep(i,,) f[i]=(f[i-]+f[i-])%MOD;
     while(cas--)
     {
         int n=read(),x=read(),y=read();
         if(x>) x++;
         if(y<n) y--;
         printf("%d\n",f[y-x+]);
     }

     return ;
 }