很优雅的代码（把时间复杂度控到22）

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll INF = 1e18;

struct Edge{
int u,v;
ll w,b;
}e[5005];

vector<pair<int,ll>> g[5005];
int n,m;

void spfa(vector<ll>& dis, const vector<int>& sources){
queue<int> q;
vector<bool> inq(n+1,false);
for(int x : sources){
if(!inq[x]){
q.push(x);
inq[x]=true;
}
}
while(!q.empty()){
int u = q.front(); q.pop();
inq[u]=false;
for(auto &pr : g[u]){
int to = pr.first;
ll w = pr.second;
if(dis[to] > dis[u] + w){
dis[to] = dis[u] + w;
if(!inq[to]){
inq[to]=true;
q.push(to);
}
}
}
}
}

int main(){
ios::sync_with_stdio(false);
cin.tie(0);
cin>>n>>m;
for(int i=0;i<m;i++){
cin>>e[i].u>>e[i].v>>e[i].w>>e[i].b;
}
sort(e,e+m,[](const Edge&a,const Edge&b){return a.b < b.b;});

vector<ll> d1(n+1,INF);
vector<ll> dn(n+1,INF);
d1[1]=0;
dn[n]=0;

ll ans = INF;
int ptr=0;
while(ptr<m){
    int curB = e[ptr].b;
    int j=ptr;
    vector<int> src;
    while(j<m && e[j].b == curB){
        int u=e[j].u, v=e[j].v; ll w=e[j].w;
        g[u].emplace_back(v,w);
        g[v].emplace_back(u,w);
        src.push_back(u);
        src.push_back(v);
        j++;
    }
    spfa(d1, src);
    spfa(dn, src);

    for(int k=ptr;k<j;k++){
        int u=e[k].u, v=e[k].v;
        ll op1=INF,op2=INF;
        if(d1[u]!=INF && dn[v]!=INF) op1 = d1[u]+dn[v];
        if(d1[v]!=INF && dn[u]!=INF) op2 = d1[v]+dn[u];
        ans = min(ans, min(op1,op2));
    }
    ptr=j;
}
if(ans>=INF) cout<<-1<<endl;
else cout<<ans<<endl;
return 0;

}