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;
#define m_p make_pair
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define fi first
#define se second
typedef long long ll;
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
mt19937 rnf(2106);
const int N = 500005, M = 1000000007;
int n, m;
int a[N];
vector<int> v[N];
int dp[N][26][2];
void solv()
{
cin >> n >> m;
for (int i = 1; i <= m; ++i)
{
int x, y;
cin >> x >> y;
if (x == y)
continue;
if (x < y)
{
v[x].push_back(y);
}
else
{
v[y].push_back(-x);
}
}
stack<int> g[2];
int s[26] = {};
for (int k = 0; k < 26; ++k)
{
dp[n][k][0] = 1;
s[k] = 1;
}
for (int i = n - 1; i >= 1; --i)
{
/*for (int k = 0; k < 26; ++k)
{
for (int j = i + 1; j <= n; ++j)
{
s[k] = (s[k] + dp[j][k][0]) % M;
s[k] = (s[k] + dp[j][k][1]) % M;
}
}*/
int p[26] = {};
p[0] = s[0];
for (int k = 1; k < 26; ++k)
p[k] = (p[k - 1] + s[k]) % M;
for (int k = 0; k < 26; ++k)
{
dp[i][k][1] = (p[25] - p[k] + M) % M;
if (k)
dp[i][k][0] = p[k - 1];
s[k] = (s[k] + dp[i][k][1]) % M;
s[k] = (s[k] + dp[i][k][0]) % M;
/*for (int u = k + 1; u < 26; ++u)
dp[i][k][1] = (dp[i][k][1] + s[u]) % M;
for (int u = 0; u < k; ++u)
dp[i][k][0] = (dp[i][k][0] + s[u]) % M;*/
}
g[0].push(i);
g[1].push(i);
for(int t = 0; t < sz(v[i]); ++t)
{
if (v[i][t] > 0)
{
while (!g[1].empty())
{
int j = g[1].top();
if (j < v[i][t])
{
for (int k = 0; k < 26; ++k)
{
s[k] = (s[k] - dp[j][k][1] + M) % M;
dp[j][k][1] = 0;
}
g[1].pop();
}
else
break;
}
}
else
{
while (!g[0].empty())
{
int j = g[0].top();
if (j < -v[i][t])
{
for (int k = 0; k < 26; ++k)
{
s[k] = (s[k] - dp[j][k][0] + M) % M;
dp[j][k][0] = 0;
}
g[0].pop();
}
else
break;
}
}
}
}
int ans = 0;
for (int k = 0; k < 26; ++k)
ans = (ans + s[k]) % M;
cout << ans << "\n";
}
int main()
{
#ifdef SOMETHING
freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);
#endif // SOMETHING
ios_base::sync_with_stdio(false), cin.tie(0);
int tt = 1;
//cin >> tt;
while (tt--)
{
solv();
}
return 0;
}
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