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;
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 = 20005;
const int MOD = 1000000007;
int n, m;
int lr[MAXN][2];
ll dp[2][MAXN][30];
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);
}
int cur = 1, prv = 0;
REP (c, 0, 26) {
dp[cur][1][c] = 1;
}
REP (i, 2, n + 1) {
swap(cur, prv);
memset(dp[cur], 0, sizeof dp[cur]);
int r[2] = {0, 0};
RREP (j, i - 1, 1) {
REP (z, 0, 2) {
mxto(r[z], lr[j][z]);
}
REP (c, 0, 26) {
// stay the same
dp[cur][j][c] += dp[prv][j][c];
if (dp[cur][j][c] >= MOD) {
dp[cur][j][c] -= MOD;
}
REP (nc, 0, 26) {
if (c == nc) continue;
if (r[0] >= i && c < nc) {
continue;
}
if (r[1] >= i && c > nc) {
continue;
}
dp[cur][i][nc] += dp[prv][j][c];
if (dp[cur][i][nc] >= MOD) {
dp[cur][i][nc] -= 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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