感觉链表前向星好危险，求个hack

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
#define f(i, x, y, ...) for (int i = x, ##__VA_ARGS__; i <= y; ++i)
template <class T>
class FS
{
public:
    struct Line
    {
        int u, v;
        T w;
        Line *next = nullptr, *prev = nullptr;
        Line(int U, int V, T W) : u(U), v(V), w(W) {}
    };
    vector<Line *> head;
public:
    FS(size_t sz) : head(sz) {}
    void add(int u, int v, T w)
    {
        Line *newedge = new Line(u, v, w);
        if (head[u])head[u]->prev = newedge, newedge->next = head[u];
        head[u] = newedge;
    }
    Line *&operator[](int u)
    {
        return head[u];
    }
};
constexpr int maxn = 1e4 + 5, inf = LLONG_MAX;
vector<pair<int, int>> nodes;
vector<double> dis(maxn, inf);
vector<bool> vis(maxn);
FS<double> head(maxn);
vector<FS<double>::Line *> pre(maxn), path;
int n, m;
double ans = inf;
void dij1()
{
    priority_queue<tuple<double, int, int>, vector<tuple<double, int, int>>, greater<tuple<double, int, int>>> q;
    q.push({0, 1, 0});
    while (q.size())
    {
        auto [d, u, lst] = q.top();
        q.pop();
        if (d > dis[u])continue;
        dis[u] = d, vis[u] = 1;
        for (auto i = head[u]; i; i = i->next)
            if (dis[i->v] > dis[u] + i->w)
            {
                dis[i->v] = dis[u] + i->w;
                if (!vis[i->v])
                    q.push({dis[i->v], i->v, u}), pre[i->v] = i;
            }
    }
}
void get_path()
{
    for (auto i = pre[n]; i; i = pre[i->u])path.push_back(i);
}
double dij2()
{
    priority_queue<pair<double, int>, vector<pair<double, int>>, greater<pair<double, int>>> q;
    vector<double> dis(n + 1, inf);
    vector<bool> vis(n + 1);
    q.push({0, 1});
    while (q.size())
    {
        auto [d, u] = q.top();
        q.pop();
        if (d > dis[u])continue;
        dis[u] = d, vis[u] = 1;
        for (auto i = head[u]; i; i = i->next)
            if (dis[i->v] > dis[u] + i->w)
            {
                dis[i->v] = dis[u] + i->w;
                if (!vis[i->v])
                    q.push({dis[i->v], i->v});
            }
    }
    return dis[n];
}
signed main()
{
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    cin >> n >> m;
    f(i, 1, n, x, y)cin >> x >> y,nodes.emplace_back(x, y);
    f(i, 1, m, p, q)cin >> p >> q,head.add(p, q, sqrt((nodes[p - 1].first - nodes[q - 1].first) * (nodes[p - 1].first - nodes[q - 1].first) + (nodes[p - 1].second - nodes[q - 1].second) * (nodes[p - 1].second - nodes[q - 1].second))),head.add(q, p, sqrt((nodes[p - 1].first - nodes[q - 1].first) * (nodes[p - 1].first - nodes[q - 1].first) + (nodes[p - 1].second - nodes[q - 1].second) * (nodes[p - 1].second - nodes[q - 1].second)));
    dij1(),get_path();
    for (auto i : path)
    {
        if (i->prev)i->prev->next = i->next;
        if (i->next)i->next->prev = i->prev;
        if (head[i->u] == i)head[i->u] = i->next;
        ans = min(ans, dij2());
        if (i->prev)i->prev->next = i;
        if (i->next)i->next->prev = i;
        if (head[i->u] == i->next)head[i->u] = i;
    }
    printf("%.2f", ans);
    return 0;
}