bzoj3669【NOI2014】魔法森林 SPFA

调了一整个晚上一脸懵逼，加了个并查集优化就WA了= =，然而并没能发现

题意就是两个点权的最短路，标准做法LCT维护，当然我们考虑这是随机数据，我们可以用SPFA水

枚举其中一个点权，然后做另外一个点权的最短路，同时需要用许多优化防止TLE

比如因为单调性，于是每次SPFA并不需要把dis数组清0，用优先队列来维护每一次放进去的点不然写起来全是WA之类的

/**************************************************************
Problem: 3669
User: BPM136
Language: C++
Result: Accepted
Time:3032 ms
Memory:8680 kb
****************************************************************/

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<bitset>
#include<queue>
#define LL long long
#define fo(i,a,b) for(int i=a;i<=b;i++)
#define down(i,a,b) for(int i=a;i>=b;i--)
#define efo(i,x) for(int i=last[x];i!=0;i=e[i].next)
using namespace std;
inline LL read()
{
LL d=0,f=1;char s=getchar();
while(s<'0'||s>'9'){if(s=='-')f=-1;s=getchar();}
while(s>='0'&&s<='9'){d=d*10+s-'0';s=getchar();}
return d*f;
}
#define N 50005
#define M 100005
#define inf 1000000007
struct hhx
{
int f,v;
hhx(int a,int b):f(b),v(a){}
bool operator < (const hhx& a)const
{return a.f<f;}
};
struct edge
{
int y,next,c;
}e[M*2];
struct bian
{
int u,v,a,b;
}b[M*2];
int last
,ne=0;
int n,m,ma,ans=inf;
int h=0,t=1;
int dis
;bitset<N>inq;

bool com(bian a,bian b)
{
return a.a<b.a;
}

void add(int x,int y,int c)
{
e[++ne].y=y;e[ne].c=c;e[ne].next=last[x];last[x]=ne;
}
void add2(int x,int y,int c)
{
add(x,y,c);add(y,x,c);
// cout<<"Bian:"<<min(x,y)<<' '<<max(x,y)<<' '<<c<<endl;
}

void init()
{
n=read(),m=read();int mi1=1000000,miN=1000000;
fo(i,1,m)
{
int u=read(),v=read(),va=read(),vb=read();
b[i].u=u;
b[i].v=v;
b[i].a=va;
b[i].b=vb;
if(u==1||v==1)mi1=min(mi1,va);
if(u==n||v==n)miN=min(miN,va);
}
ma=max(mi1,miN);
}

priority_queue<hhx>q;
void spfa()
{
int i,u,v;
hhx X(0,0);
while(!q.empty())
{
X=q.top();
q.pop();
u=X.v;
inq[u]=0;
efo(i,u)
{
v=e[i].y;
if(dis[v]>max(dis[u],e[i].c))
{
dis[v]=max(dis[u],e[i].c);
if(!inq[v])
{
inq[v]=1;
q.push(hhx(v,dis[v]));
}
}
}
}
}

void checkdis()
{
cout<<"DIS:";fo(i,1,n)cout<<dis[i]<<' ';cout<<endl;
}

void work()
{
sort(b+1,b+m+1,com);
add2(b[1].u,b[1].v,b[1].b);
dis[1]=0;fo(i,2,n)dis[i]=inf;
inq.reset();
fo(i,1,m)
{
if(b[i].a==b[i-1].a||i==1||b[i].a<ma)
{
add2(b[i].u,b[i].v,b[i].b);
q.push(hhx(b[i].u,dis[b[i].u])),inq[b[i].u]=1;
q.push(hhx(b[i].v,dis[b[i].v])),inq[b[i].v]=1;
continue;
}
spfa();
ans=min(ans,b[i-1].a+dis
);
add2(b[i].u,b[i].v,b[i].b);
q.push(hhx(b[i].u,dis[b[i].u])),inq[b[i].u]=1;
q.push(hhx(b[i].v,dis[b[i].v])),inq[b[i].v]=1;
}
spfa();
ans=min(ans,b[m].a+dis
);
}

int main()
{
init();
work();
if(ans==inf)cout<<-1<<endl;else cout<<ans<<endl;
return 0;
}