CF1366G. Construct the String

https://codeforces.ml/contest/1366/problem/G

这玩意↑可以点开放大看

#include <bits/stdc++.h>
using namespace std;
#define int long long
void read (int &x) {
	char ch = getchar(); x = 0;
	while (!isdigit(ch)) ch = getchar();
	while (isdigit(ch)) x = x * 10 + ch - 48, ch = getchar();
} const int N = 2038, mod = 1e9 + 7;
int n, m, q, res, mx, f[N][2];
int cnt, h[N], to[N << 1], nxt[N << 1], d[N << 1];
void add (int u, int v, int w) {
	to[++cnt] = v, d[cnt] = w, nxt[cnt] = h[u], h[u] = cnt;
}
pair<int, int> t[N];  
#define x first
#define y second
int Pow (int x, int y) {
	int tmp = 1;
	while (y) {
		if (y & 1) tmp = tmp * x % mod;
		x = x * x % mod, y >>= 1;
	} return tmp;
}
signed main() {
//	freopen ("data.in", "r", stdin);
	read (n), read (m), read (q);
	for (int i = 1, u, v, w; i <= m; ++i) {
		read (u), read (v), read (w);
		add (u, v, w), add (v, u, w); mx = max (mx, w);
	}
	for (int i = 2; i <= n; ++i) f[i][0] = -1;
	for (int k = 1; k <= m; ++k) {
		int p = (k & 1), tmp = 0;
		for (int i = 1; i <= n; ++i) {
			f[i][p] = -1; 
			for (int j = h[i]; j; j = nxt[j]) {
				if (f[to[j]][p ^ 1] >= 0)
					f[i][p] = max (f[i][p], f[to[j]][p ^ 1] + d[j]);
			}
			tmp = max (tmp, f[i][p]); 
		} res = (res + tmp) % mod;
	}
	for (int i = 1; i <= n; ++i) {
		t[i].y = f[i][m & 1];
		for (int j = h[i]; j; j = nxt[j])
			t[i].x = max (t[i].x, d[j]);
	}	
	int inv = Pow (2, mod - 2);
	sort (t + 1, t + n + 1);
	for (int i = 1; i <= n; ++i) {
		int l = 1, r = q - m;
		if (t[i].y == -1) continue;
		for (int j = 1; j < i; ++j) {
			int sx = t[i].x - t[j].x, sy = t[j].y - t[i].y;
			if (!sy) continue;
			int t = ceil (1.0 * sy / sx);
			l = max (l, t);
		}
		for (int j = i + 1; j <= n; ++j) {
			int sx = t[i].x - t[j].x, sy = t[j].y - t[i].y;
			if (!sy) { r = 0; break; }
			int t = ceil (1.0 * sy / sx) - 1;
			r = min (r, t);
		} if (l > r) continue;
		res = (res + (r - l + 1) * ((t[i].y * 2 + t[i].x * (l + r)) % mod) % mod * inv % mod) % mod;
	}
	return printf ("%lld\n", res), 0;
}