이 제출은 이전 버전의 oj.uz에서 채점하였습니다. 현재는 제출 당시와는 다른 서버에서 채점을 하기 때문에, 다시 제출하면 결과가 달라질 수도 있습니다.
#include<bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
#define int long long
int sum(int l, int r, vector<int>& pre){
if(l > r) return 0;
if(l > 0) return (pre[r] - pre[l-1] + MOD) % MOD;
else return pre[r];
}
void solve(){
int n, m; cin >> n >> m;
vector<pair<vector<int>, vector<int>>> ends(n);
for(int i = 0; i < m; i++){
int a, b; cin >> a >> b; a--; b--;
int type = 1;
if(a > b) {type = 2; swap(a, b);}
a++;
if(type == 1) ends[b].first.push_back(a); //In type 1, i is >= than i + 1.
else ends[b].second.push_back(a); //In type 2, i is <= than i + 1.
// cout << "i "<< i << " type "<< type << " a "<< a << " b "<< b << "\n";
}
vector<pair<int, int>> mx(n, {0, 0});
pair<set<int>, set<int>> curr; curr.first.insert(0); curr.second.insert(0);
for(int i = n - 1; i >= 0; i--){
curr.first.erase(i+1);
curr.second.erase(i+1);
for(int& y : ends[i].first) curr.first.insert(y);
for(int& y : ends[i].second) curr.second.insert(y);
mx[i].first = *curr.first.rbegin();
mx[i].second = *curr.second.rbegin();
}
vector<vector<int>> prefix(26, vector<int>(n, 0));
for(int i = 0; i < 26; i++) prefix[i][0] = 1;
for(int i = 1; i < n; i++){
// cout << "i "<< i << " mx "<< mx[i].first << " "<< mx[i].second << "\n";
vector<int> dp(26, 0);
for(int j = 0; j < 26; j++){
for(int q = 0; q < 26; q++){
if(q == j) continue;
if(q < j){
dp[q] = (dp[q] + sum(mx[i].second, i-1, prefix[j])) % MOD;
}else{
dp[q] = (dp[q] + sum(mx[i].first, i-1, prefix[j])) % MOD;
}
}
}
for(int j = 0; j < 26; j++){
prefix[j][i] = (prefix[j][i-1] + dp[j]) % MOD;
}
// cout << "i "<< i << endl;
// for(int j = 0; j < 26; j++){
// cout << "j "<< j << " dp " << dp[j] << "\n";
// }
}
int ans = 0;
for(int i = 0; i < 26; i++) ans = (ans + sum(0, n-1, prefix[i])) % MOD;
cout << ans << "\n";
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
// int tt; cin >> tt;
int tt = 1;
while(tt--) solve();
return 0;
}
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