2018HDU多校训练2

题目链接：https://cn.vjudge.net/contest/299050

A - Absolute

HDU - 6309

代码来源：https://cn.vjudge.net/status/#un=&OJId=HDU&probNum=6309&res=1&language=&onlyFollowee=false 题目大意：给定n个区间 [ l i , r i ] [li,ri] [li,ri]， − 10 6 ≤ l i ≤ r i ≤ 1 0 6 {-10}^{6}≤ li≤ri≤10^{6} −106≤li≤ri≤106且 l i , r i li,ri li,ri都为整数，xi为对应范围内的一个随机实数，求|∑xi|的期望。n≤15，答案对998244353取模。

#include
#include
using namespace std;
#define ll long long
const int mod=998244353;

int l[15],r[15],n;
ll quickpower(ll x,ll y)
{
	ll res=1;
	while(y){
		if(y&1) res=res*x%mod;
		y>>=1;
		x=x*x%mod; 
	}
	return res;
}
ll sgn(ll x)
{
	return x>0?1:-1;
}
ll dfs(int deep,ll x=0){
	if(deep==n){
		return quickpower(x,n+1)*sgn(x);
	}
	return ((dfs(deep+1,x+r[deep])-dfs(deep+1,x+l[deep]))%mod+mod)%mod;
}
int main()
{
	scanf("%d",&n);
	ll ans=1;
	for(int i=0;i