This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
typedef long long llo;
#define a first
#define b second
#define pb push_back
#define endl '\n'
const llo mod=1e9+7;
llo n,m;
vector<llo> pre3[500001];
llo dp[500001][26];
vector<pair<llo,llo>> pre2[500001];
llo pre[500001][26];
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin>>n>>m;
for(llo i=0;i<m;i++){
llo aa,bb;
cin>>aa>>bb;
aa--;
bb--;
llo cc=0;
if(aa>bb){
swap(aa,bb);
cc=1;
}
//c=0 next is smaller
pre3[aa].pb(cc);
pre2[bb].pb({aa,cc});
}
multiset<llo> cur;
multiset<llo> cur2;
for(llo i=0;i<n;i++){
if(i==0){
for(llo j=0;j<26;j++){
dp[i][j]=1;
}
}
llo ma=0;
llo ma2=0;
if(cur.size()){
auto j=cur.end();
j--;
ma=(*j)+1;
}
if(cur2.size()){
auto j=cur2.end();
j--;
ma2=(*j)+1;
}
//cout<<i<<":"<<ma<<":"<<ma2<<endl;
//max(ma,ma2) to i-1
//min(ma,ma2) to max(ma,ma2)-1
//rest is impossible
pair<llo,llo> cur3={max(ma,ma2),i-1};
if(cur3.a<=cur3.b){
llo su=0;
for(llo j=0;j<26;j++){
su+=(pre[cur3.b+1][j]-pre[cur3.a][j]);
if(su<0){
su+=mod;
}
if(su>=mod){
su-=mod;
}
}
for(llo j=0;j<26;j++){
dp[i][j]+=su;
if(dp[i][j]>=mod){
dp[i][j]-=mod;
}
llo cot=(pre[cur3.b+1][j]-pre[cur3.a][j]);
if(cot<0){
cot+=mod;
}
dp[i][j]-=cot;
if(dp[i][j]<0){
dp[i][j]+=mod;
}
if(dp[i][j]>=mod){
dp[i][j]-=mod;
}
}
}
/* for(llo k=max(ma,ma2);k<=i-1;k++){
llo su=0;
for(llo j=0;j<26;j++){
su+=dp[k][j];
if(su>=mod){
su-=mod;
}
}
for(llo j=0;j<26;j++){
dp[i][j]+=(su-dp[k][j]+mod);
if(dp[i][j]>=mod){
dp[i][j]-=mod;
}
if(dp[i][j]>=mod){
dp[i][j]-=mod;
}
}
}*/
cur3={min(ma,ma2),max(ma,ma2)-1};
if(cur3.a<=cur3.b){
if(ma<ma2){
//no restrictions x>y
llo su=0;
for(llo j=25;j>=0;j--){
dp[i][j]+=su;
if(dp[i][j]>=mod){
dp[i][j]-=mod;
}
//cout<<cur3.a<<",,"<<cur3.b+1<<endl;
llo cot=pre[cur3.b+1][j]-pre[cur3.a][j]+mod;
if(cot>=mod){
cot-=mod;
}
su+=cot;
if(su>=mod){
su-=mod;
}
}
}
else{
//x>y always
llo su=0;
for(llo j=0;j<26;j++){
dp[i][j]+=su;
if(dp[i][j]>=mod){
dp[i][j]-=mod;
}
llo cot=pre[cur3.b+1][j]-pre[cur3.a][j];
if(cot<0){
cot+=mod;
}
su+=cot;
if(su>=mod){
su-=mod;
}
}
}
}
/* for(llo k=min(ma,ma2);k<=max(ma,ma2)-1;k++){
if(ma<ma2){
//no restrictions x>y
llo su=0;
for(llo j=25;j>=0;j--){
dp[i][j]+=su;
if(dp[i][j]>=mod){
dp[i][j]-=mod;
}
su+=dp[k][j];
if(su>=mod){
su-=mod;
}
}
}
else{
//x>y always
llo su=0;
for(llo j=0;j<26;j++){
dp[i][j]+=su;
if(dp[i][j]>=mod){
dp[i][j]-=mod;
}
su+=dp[k][j];
if(su>=mod){
su-=mod;
}
}
}
}*/
/* if(ma<ma2){
}
else if(ma>ma2){
}
*/
for(auto j:pre3[i]){
if(j==0){
cur.insert(i);
}
else{
cur2.insert(i);
}
}
for(auto j:pre2[i]){
if(j.b==1){
auto jj=cur2.find(j.a);
cur2.erase(jj);
}
else{
auto jj=cur.find(j.a);
cur.erase(jj);
}
}
for(int j=0;j<26;j++){
pre[i+1][j]=pre[i][j]+dp[i][j];
if(pre[i+1][j]>=mod){
pre[i+1][j]-=mod;
}
}
}
llo ans=0;
for(llo i=0;i<n;i++){
for(llo j=0;j<26;j++){
//cout<<i<<":"<<j<<":"<<dp[i][j]<<endl;
ans=(ans+dp[i][j]);
if(ans>=mod){
ans-=mod;
}
}
}
cout<<ans<<endl;
return 0;
}
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