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;
#ifdef Nero
#include "Deb.h"
#else
#define debug(...)
#endif
const int A = 26;
const int N = 5e5 + 5;
const int md = (int) 1e9 + 7;
int dp[N][A];
vector<int> smaller[N], bigger[N];
void add(int& a, int b) {
a += b;
if (a >= md) a -= md;
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, m;
cin >> n >> m;
for (int i = 0; i < m; ++i) {
int a, b;
cin >> a >> b;
if (a < b) {
smaller[a].push_back(a);//1
smaller[b].push_back(-a);//1
} else {
bigger[b].push_back(b);//2
bigger[a].push_back(-b);//2
}
}
for (int i = 0; i < A; ++i) {
dp[1][i] = 1;
}
vector<multiset<int>> se(3);
for (int i = 1; i <= n; ++i) {
int mx1 = 0, mx2 = 0;
if (!se[1].empty()) mx1 = max(0, *se[1].rbegin());
if (!se[2].empty()) mx2 = max(0, *se[2].rbegin());
int mx = max(mx1, mx2);
int mn = min(mx1, mx2);
for (int j = 0; j < A; ++j) {
for (int l = 0; l < A; ++l) {
for (int k = mx + 1; k < i; ++k) {
if (l != j) {
add(dp[i][j], dp[k][l]);
}
}
int st = (mx1 == mx ? 1 : 0) | (mx2 == mx ? 2 : 0);
for (int k = mn + 1; k <= mx; ++k) {
add(dp[i][j], dp[k][l] * (st & 1 ? l < j: 1) * (st & 2 ? l > j : 1));
}
}
}
for (int x : smaller[i]) {
if (x > 0) se[1].insert(x);
else se[1].erase(se[1].find(-x));
}
for (int x : bigger[i]) {
if (x > 0) se[2].insert(x);
else se[2].erase(se[2].find(-x));
}
}
int ans = 0;
for (int i = 1; i <= n; ++i) {
for (int j = 0; j < A; ++j) {
add(ans, dp[i][j]);
}
}
cout << ans << '\n';
return 0;
}
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