ask：关于时间复杂度

#include<bits/stdc++.h>
using namespace std;
using ll=long long;
#define int long long
const int N=4e5+12;
const ll inf=0x3f3f3f3f3f3f3f3f;
int n,m;
int head[N],to[N<<1],nex[N<<1],tp[N<<1],tot=0;//tp:temperature
inline void mkr(int u,int v,int w){
	to[++tot]=v,nex[tot]=head[u],tp[tot]=w,head[u]=tot;
}
struct node_edge1{
	int fr,to;
	bool operator < (const node_edge1 &oth) const{
		if(fr==oth.fr){
			return to<oth.to;
		}
		return fr<oth.fr;
	}
};
map<node_edge1,ll> dis;
map<node_edge1,bool> vis;
int a,b,c;
struct node{
	int fr,to,tp;ll dis;
	bool operator < (const node &oth) const{
		return dis>oth.dis;
	}
	node(){}
	node(int _fr,int _to,int _tp,int _dis){
		fr=_fr,to=_to,tp=_tp,dis=_dis;
	}
};
priority_queue<node> q;
signed main(){
	cin>>n>>m;
	for(int i=1;i<=m;i++){
		cin>>a>>b>>c;
		dis[{a,b}]=dis[{b,a}]=inf;
		mkr(a,b,c),mkr(b,a,c);
	}
	for(int f=head[1];f;f=nex[f]){
		int t=to[f],v=tp[f];
//		cout<<"bg 1 "<<t<<' '<<v<<endl;
		dis[{1,t}]=v;
		q.emplace(1,t,v,v);
	}
//	for(auto ff:dis){
//		cout<<"edge "<<ff.first.fr<<' '<<ff.first.to<<' '<<ff.second<<endl;
//	}
	while(!q.empty()){
		node now=q.top();q.pop();
		if(vis[{now.fr,now.to}])continue;
		vis[{now.fr,now.to}]=1;
		for(int f=head[now.to];f;f=nex[f]){
			int t=to[f],v=abs(now.tp-tp[f]);
			if(dis[{now.to,t}]>now.dis+v){
				dis[{now.to,t}]=now.dis+v;
				q.emplace(now.to,t,tp[f],now.dis+v);
			}
		}
	}
	ll ans=inf;
//	for(auto ff:dis){
//		cout<<"edge "<<ff.first.fr<<' '<<ff.first.to<<' '<<ff.second<<endl;
//	}
	for(int f=head[n];f;f=nex[f]){
		ans=min(ans,dis[{to[f],n}]);
	}
	cout<<ans<<endl;
	return 0;
}