使用k次半价，求最小花费

#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int MAXN = 10005;
const ll inf = 1e18 + 7;
struct edge
{
	int to;
	ll w;
	int nex;
}e[50000 * 2];
int head[MAXN], tot;
int n, m, k;
void add(int a, int b, ll c)
{
	e[tot] = edge{ b,c,head[a] };
	head[a] = tot++;
}
ll dis[MAXN][12];
bool vis[MAXN][12];
struct node
{
	int now;
	ll w;
	int cnt;
};
auto cmp = [](node q, node w) {
	return q.w > w.w;
};
void dij()
{
	priority_queue<node, vector<node>, decltype(cmp) >q(cmp);
	q.push(node{ 1,0,0 });
	dis[1][0] = 0;
	while (!q.empty())
	{
		node temp = q.top();
		q.pop();
		if (vis[temp.now][temp.cnt])
			continue;
		vis[temp.now][temp.cnt] = true;
		for (int i = head[temp.now]; i + 1; i = e[i].nex)
		{
			int t = e[i].to;
			if (dis[t][temp.cnt] > dis[temp.now][temp.cnt] + e[i].w)
			{
				dis[t][temp.cnt] = dis[temp.now][temp.cnt] + e[i].w;
				q.push(node{ t,dis[t][temp.cnt],temp.cnt });
			}
			if (dis[t][temp.cnt + 1] > dis[temp.now][temp.cnt] + e[i].w / 2)
			{
				if (temp.cnt > 10)
					continue;
				dis[t][temp.cnt + 1] = dis[temp.now][temp.cnt] + e[i].w / 2;
				q.push(node{ t,dis[t][temp.cnt + 1],temp.cnt + 1 });
			}
		}
	}
	//printf("%lld\n", dis[n]);
}
void init()
{
	for (int i = 0; i < MAXN; i++)
		for (int j = 0; j < 12; j++)
			dis[i][j] = inf;
	memset(head, -1, sizeof(head));
	tot = 1;
}
int main()
{
	init();
	scanf("%d%d%d", &n, &m, &k);
	while (m--)
	{
		int a, b;
		ll c;
		scanf("%d%d%lld", &a, &b, &c);
		add(a, b, c);
	}
	dij();
	ll ans = inf;
	for (int i = 0; i <= k; i++)
	{
		ans = min(ans, dis[n][i]);
	}
	printf("%lld\n", ans);
}

构造虚拟节点表示上车和下车的状态

code:

#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int MAXN = 6e5;
const ll mod = 1e9 + 7;
const ll inf = 1e18 + 7;
struct edge
{
	int to;
	ll w;
	int nex;
}e[MAXN * 2];
int head[MAXN], tot;
ll dis[MAXN];
bool vis[MAXN];
void init()
{
	memset(head, -1, sizeof(head));
	tot = 1;
	for (int i = 0; i < MAXN; i++)
		dis[i] = inf;
}
void add(int a, int b, ll c)
{
	e[tot] = edge{ b,c,head[a] };
	head[a] = tot++;
}
#define Pair pair<int,int>
void dij(int s)
{
	priority_queue<Pair, vector<Pair>, greater<Pair> >q;
	q.push(Pair{ 0,s });
	dis[s] = 0;
	while (!q.empty())
	{
		int u = q.top().second;
		q.pop();
		if (vis[u])
			continue;
		vis[u] = true;
		for (int i = head[u]; i + 1; i = e[i].nex)
		{
			int v = e[i].to;
			if (dis[v] > dis[u] + e[i].w)
			{
				dis[v] = dis[u] + e[i].w;
				q.push(Pair{ dis[v],v });
			}
		}
	}
}
int n, m, s, t;
int in[1005];
int main()
{
	init();
	scanf("%d%d%d%d", &n, &m, &s, &t);
	int a, b, cnt;
	for (int i = 0; i < m; i++)
	{
		scanf("%d%d%d", &a, &b, &cnt);
		for (int j = 0; j < cnt; j++)
		{
			scanf("%d", &in[j]);
			if (j > 0)
			{
				add(i * n + in[j - 1], i * n + in[j], b);
				add(i * n + in[j], i * n + in[j - 1], b);
			}
			add(i * n + in[j], m * n + in[j], 0);
			add(m * n + in[j], i * n + in[j], a);
		}
	}
	dij(m * n + s);
	if (dis[m * n + t] == inf)
		dis[m * n + t] = -1;
	printf("%lld\n", dis[m * n + t]);
}