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>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
namespace x = __gnu_pbds;
template <typename T>
using ordered_set = x::tree<T, x::null_type, less<T>, x::rb_tree_tag, x::tree_order_statistics_node_update>;
template <typename T>
using normal_queue = priority_queue<T, vector<T>, greater<>>;
#define all(x) begin(x), end(x)
#define sz(x) ((int) (x).size())
#define x first
#define y second
using ll = long long;
using ld = long double;
#define int ll
const int N = 1 << 19, C = 26, MOD = 1e9 + 7;
int dp[N][C + 1], t[2][2 * N];
signed main() {
cin.tie(0)->sync_with_stdio(0);
int n, m;
cin >> n >> m;
fill(t[0], t[2], -1);
for (int i = 0; i < m; ++i) {
int u, v;
cin >> u >> v;
--u, --v;
int l = N + min(u, v) + 1, r = N + max(u, v);
bool at = u > v;
while (l <= r) {
if (l & 1) t[at][l] = max(t[at][l], min(u, v));
if (!(r & 1)) t[at][r] = max(t[at][r], min(u, v));
l = (l + 1) / 2;
r = (r - 1) / 2;
}
}
for (int i = 0; i < 2; ++i) {
for (int j = 0; j < N; ++j) {
t[i][2 * j] = max(t[i][2 * j], t[i][j]);
t[i][2 * j + 1] = max(t[i][2 * j + 1], t[i][j]);
}
}
for (int i = 0; i < n; ++i) {
for (int j = 0; j < C; ++j) {
dp[i][j] = 0;
}
}
for (int i = 0; i < C; ++i) {
dp[n - 1][i] = 1;
}
for (int i = n - 1; i > 0; --i) {
for (int j = 0; j < C; ++j) {
(dp[i][j] += dp[i + 1][j]) %= MOD;
}
for (int c0 = 0; c0 < C; ++c0) {
int j0 = t[0][N + i], j1 = t[1][N + i];
for (int c1 = 0; c1 < C; ++c1) {
if (c0 != c1) {
(dp[i - 1][c1] += dp[i][c0]) %= MOD;
(dp[max(j0, j1)][c1] -= dp[i][c0]) %= MOD;
// for (int j = max(j0, j1) + 1; j < i; ++j) {
// (dp[j][c1] += dp[i][c0]) %= MOD;
// }
}
}
if (j0 < j1) {
for (int c1 = 0; c1 < c0; ++c1) {
(dp[max(j0, j1)][c1] += dp[i][c0]) %= MOD;
(dp[min(j0, j1)][c1] -= dp[i][c0]) %= MOD;
// for (int j = min(j0, j1) + 1; j <= max(j0, j1); ++j) {
// (dp[j][c1] += dp[i][c0]) %= MOD;
// }
}
} else {
for (int c1 = c0 + 1; c1 < C; ++c1) {
(dp[max(j0, j1)][c1] += dp[i][c0]) %= MOD;
(dp[min(j0, j1)][c1] -= dp[i][c0]) %= MOD;
// for (int j = min(j0, j1) + 1; j <= max(j0, j1); ++j) {
// (dp[j][c1] += dp[i][c0]) %= MOD;
// }
}
}
}
}
for (int j = 0; j < C; ++j) {
(dp[0][j] += dp[1][j]) %= MOD;
}
cout << (accumulate(dp[0], dp[1], 0ll) % MOD + MOD) % MOD;
}
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