Submission #546644

#TimeUsernameProblemLanguageResultExecution timeMemory
546644inksamuraiMisspelling (JOI22_misspelling)C++17
100 / 100
2332 ms415804 KiB
#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
#define rng(i,x,n) for(int i=x;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define fi first
#define se second
#define pb push_back
#define sz(a) (int)a.size()
#define vec(...) vector<__VA_ARGS__>
#define _3x2WzQf ios::sync_with_stdio(0),cin.tie(0)
typedef long long ll;
using pii=pair<int,int>;
using vi=vector<int>;
void print(){cout<<'\n';}
template<class h,class...t>
void print(const h&v,const t&...u){cout<<v<<' ',print(u...);}
// e
 
 
//snuke's mod int
template <ll mod>
struct modint{
	ll x; // typedef long long ll;
	modint(ll x=0):x((x%mod+mod)%mod){}
	modint operator-()const{return modint(-x);}
	modint& operator+=(const modint a){if((x+=a.x)>=mod) x-=mod; return *this;}
	modint& operator-=(const modint a){if((x+=mod-a.x)>=mod) x-=mod; return *this;}
	modint& operator*=(const modint a){(x*=a.x)%=mod; return *this;}
	modint operator+(const modint a)const{modint res(*this); return res+=a;}
	modint operator-(const modint a)const{modint res(*this); return res-=a;}
	modint operator*(const modint a)const{modint res(*this); return res*=a;}
	modint pow(ll n)const{
		modint res=1,x(*this);
		while(n){
			if(n&1)res*=x;
			x*=x;
			n>>=1;
		}
		return res;
	}
	modint inv()const{return pow(mod-2);}
};
 
using mint=modint<1000'000'007>;
 
mint dp[30][2],fdp[30][2];
 
signed main(){
_3x2WzQf;
	int n,m;
	cin>>n>>m;
 
	vec(vi) qry(n,vi(2,-1));
	rep(i,m){
		int l,r;
		cin>>l>>r;
		l-=1,r-=1;
		bool type=0;
		if(l>r){
			swap(l,r);
			type=1;
		}
		qry[l][type]=max(qry[l][type],r);
	}
 
	using tup=tuple<int,int,mint>;
	deque<tup> dq0,dq1;
 
	per(ch,26){
		dp[ch][0]=1;
	}
	per(i,n-1){
		int r0=qry[i][0];
		int r1=qry[i][1];
		rep(x,26){
			rep(y,26){
				if(x==y) continue;
				if(r0!=-1 and y>x) continue;
				if(r1!=-1 and y<x) continue;
				rep(t,2){
					int nt=(y>x?1:0);
					fdp[y][nt]+=dp[x][t];
				}
			}
		}
		rep(y,26){
			rep(nt,2){
				if(nt) dq1.pb({i,y,fdp[y][nt]});
				else dq0.pb({i,y,fdp[y][nt]});
				dp[y][nt]+=fdp[y][nt];
				fdp[y][nt]=0;
			}
		}
		while(sz(dq1)){
			auto &[j,ch,val]=dq1.back();
			if(j<r0){
				dp[ch][1]-=val;
				dq1.pop_back();
			}else{
				break;
			}
		}
		while(sz(dq0)){
			auto &[j,ch,val]=dq0.back();
			if(j<r1){
				dp[ch][0]-=val;
				dq0.pop_back();
			}else{
				break;
			}
		}
	}
 
	mint ans=0;
	rep(x,26){
		rep(t,2){
			ans+=dp[x][t];
		}
	}
 
	print(ans.x);
//	
	return 0;
}
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