이 제출은 이전 버전의 oj.uz에서 채점하였습니다. 현재는 제출 당시와는 다른 서버에서 채점을 하기 때문에, 다시 제출하면 결과가 달라질 수도 있습니다.
// Hallelujah, praise the one who set me free
// Hallelujah, death has lost its grip on me
// You have broken every chain, There's salvation in your name
// Jesus Christ, my living hope
#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
template <class T>
inline bool mnto(T& a, T b) {return a > b ? a = b, 1 : 0;}
template <class T>
inline bool mxto(T& a, T b) {return a < b ? a = b, 1: 0;}
#define REP(i, s, e) for (int i = s; i < e; i++)
#define RREP(i, s, e) for (int i = s; i >= e; i--)
typedef long long ll;
typedef long double ld;
#define FI first
#define SE second
typedef pair<int, int> ii;
typedef pair<ll, ll> pll;
typedef tuple<int, int, int> iii;
#define ALL(_a) _a.begin(), _a.end()
#define SZ(_a) (int) _a.size()
#define pb push_back
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<ii> vii;
typedef vector<iii> viii;
#ifndef DEBUG
#define cerr if (0) cerr
#endif
const int INF = 1000000005;
const ll LINF = 1000000000000000005ll;
const int MAXN = 500005;
const int MOD = 1000000007;
int n, m;
int lr[MAXN][2];
//ll dp[2][MAXN][30];
ll dp[MAXN][30], psm[MAXN][30], rowsm[30][MAXN];
ll ans;
int main() {
#ifndef DEBUG
ios::sync_with_stdio(0), cin.tie(0);
#endif
cin >> n >> m;
REP (i, 0, m) {
int a, b; cin >> a >> b;
bool s = 0;
if (a > b) {
s = 1;
swap(a, b);
}
mxto(lr[a][s], b);
}
REP (c, 0, 26) {
dp[1][c] = 1;
psm[1][c] = c + 1;
rowsm[c][1] = c + 1;
}
vii stk[2];
int ptr[2] = {0, 0};
REP (i, 2, n + 1) {
REP (z, 0, 2) {
while (!stk[z].empty() && stk[z].back().FI < lr[i - 1][z]) {
stk[z].pop_back();
}
stk[z].pb({lr[i - 1][z], i - 1});
while (ptr[z] >= SZ(stk[z]) ||
(ptr[z] >= 0 && stk[z][ptr[z]].FI < i)) {
ptr[z]--;
}
while (ptr[z] + 1 < SZ(stk[z]) && stk[z][ptr[z] + 1].FI >= i) {
ptr[z]++;
}
// increment range (stk[z][ptr[z]].SE, i - 1]
int s = ptr[z] < 0 ? -1 : stk[z][ptr[z]].SE; // exclusive
REP (c, 0, 26) {
ll fi, se;
if (z) {
if (c) {
fi = rowsm[c - 1][i - 1];
se = (s < 0 ? 0 : rowsm[c - 1][s]);
} else {
fi = 0;
se = 0;
}
} else {
fi = rowsm[25][i - 1] - rowsm[c][i - 1];
se = (s < 0 ? 0 : (rowsm[25][s] - rowsm[c][s]));
if (fi < 0) {
fi += MOD;
}
if (se < 0) {
se += MOD;
}
}
dp[i][c] += fi - se;
if (dp[i][c] < 0) {
dp[i][c] += MOD;
}
if (dp[i][c] >= MOD) {
dp[i][c] -= MOD;
}
}
}
psm[i][0] = dp[i][0];
REP (c, 1, 26) {
psm[i][c] = psm[i][c - 1] + dp[i][c];
if (psm[i][c] >= MOD) {
psm[i][c] -= MOD;
}
}
REP (c, 0, 26) {
rowsm[c][i] = rowsm[c][i - 1] + psm[i][c];
if (rowsm[c][i] >= MOD) {
rowsm[c][i] -= MOD;
}
}
}
REP (j, 1, n + 1) {
REP (c, 0, 26) {
ans += dp[j][c];
if (ans >= MOD) {
ans -= MOD;
}
}
}
/*
int cur = 1, prv = 0;
REP (c, 0, 26) {
dp[cur][1][c] = 1;
}
REP (i, 2, n + 1) {
swap(cur, prv);
int r[2] = {0, 0};
RREP (j, i - 1, 1) {
mxto(r[0], lr[j][0]);
mxto(r[1], lr[j][1]);
ll lsm = 0, rsm = 0;
REP (c, 0, 26) {
rsm += dp[prv][j][c];
if (rsm >= MOD) {
rsm -= MOD;
}
// stay the same
dp[cur][j][c] = dp[prv][j][c];
}
REP (c, 0, 26) {
rsm -= dp[prv][j][c];
if (rsm < 0) {
rsm += MOD;
}
if (r[0] < i) {
dp[cur][i][c] += rsm;
if (dp[cur][i][c] >= MOD) {
dp[cur][i][c] -= MOD;
}
}
if (r[1] < i) {
dp[cur][i][c] += lsm;
if (dp[cur][i][c] >= MOD) {
dp[cur][i][c] -= MOD;
}
}
lsm += dp[prv][j][c];
if (lsm >= MOD) {
lsm -= MOD;
}
}
}
}
REP (j, 1, n + 1) {
REP (c, 0, 26) {
ans += dp[cur][j][c];
if (ans >= MOD) {
ans -= MOD;
}
}
}
*/
cout << ans << '\n';
return 0;
}
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