bzoj3669【NOI2014】魔法森林 SPFA

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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 1000000007struct 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[N],ne=0;int n,m,ma,ans=inf;int h=0,t=1;int dis[N];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[n]);        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[n]);} int main(){    init();    work();    if(ans==inf)cout<<-1<<endl;else cout<<ans<<endl;    return 0;}

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