• BZOJ 1977 次小生成树


    TM终于过了。。。。

    #include<iostream>
    #include<cstdio>
    #include<cstring>
    #include<algorithm>
    #define maxv 300500
    #define maxe 800500
    #define inf 0x7fffffffffffffff
    using namespace std;
    struct edge
    {
        long long v,w,nxt;
    }e[maxe];
    struct edge_mp
    {
        long long u,v,w,flag;
    }mp[maxe];
    long long n,m,g[maxv],nume=0,father[maxv],anc[maxv][22],mx1[maxv][22],mx2[maxv][22],ans=0,dx=inf,dis[maxv];
    long long r1=0,r2=0;
    bool cmp(edge_mp x,edge_mp y)
    {
        return x.w<y.w;
    }
    void addedge(long long u,long long v,long long w)
    {
        e[++nume].v=v;
        e[nume].w=w;
        e[nume].nxt=g[u];
        g[u]=nume;
    }
    long long getfather(long long x)
    {
        if (father[x]!=x) 
            father[x]=getfather(father[x]);
        return father[x];
    }
    void kruskal()
    {
        for (long long i=1;i<=n;i++) father[i]=i;
        sort(mp+1,mp+m+1,cmp);
        for (long long i=1;i<=m;i++)
        {
            long long u=mp[i].u,v=mp[i].v,w=mp[i].w;
            if (getfather(u)!=getfather(v))
            {
                father[getfather(u)]=getfather(v);mp[i].flag=1;ans+=w;
                addedge(u,v,w);addedge(v,u,w);
            }
        }
    }
    void dfs(long long x,long long father)
    {
        for (long long i=g[x];i;i=e[i].nxt)
        {
            long long v=e[i].v;
            if (v!=father)
            {
                anc[v][0]=x;mx1[v][0]=e[i].w;mx2[v][0]=0;
                dis[v]=dis[x]+1;
                dfs(v,x);
            }
        }
    }
    void get_table()
    {
        for (long long e=1;e<=20;e++)
            for (long long i=1;i<=n;i++)
            {
                anc[i][e]=anc[anc[i][e-1]][e-1];
                long long regis[5];
                regis[1]=mx1[i][e-1];regis[2]=mx1[anc[i][e-1]][e-1];
                regis[3]=mx2[i][e-1];regis[4]=mx2[anc[i][e-1]][e-1];
                sort(regis+1,regis+5);
                mx1[i][e]=regis[4];
                for (long long j=3;j>=1;j--)
                {
                    if (regis[j]==regis[j+1]) continue;
                    else {mx2[i][e]=regis[j];break;}
                }
            }
    }
     
    void get_ans(long long x)
    {
        long long u=mp[x].u,v=mp[x].v;r1=-1;r2=-1;
        long long k1=-1,k2=-1,k3=-1,k4=-1;
        if (dis[u]<dis[v]) swap(u,v);
        if (dis[u]!=dis[v])
        {
            for (long long e=20;e>=0;e--)
            {
                long long pos=anc[u][e];
                if ((dis[pos]>=dis[v]) && (pos>0))
                {
                    long long regis[5];
                    regis[1]=mx1[u][e];regis[2]=mx2[u][e];regis[3]=k1;regis[4]=k2;
                    sort(regis+1,regis+5);
                    k1=regis[4];
                    for (long long i=3;i>=1;i--)
                    {
                        if (regis[i]==regis[i+1]) continue;
                        else {k2=regis[i];break;}
                    }
                    u=pos;
                }
            }
        }
        if (u==v)
        {
            r1=k1;r2=k2;
            return;
        }
        for (long long e=20;e>=0;e--)
        {
            long long posu=anc[u][e],posv=anc[v][e];
            if (posu!=posv)
            {
                long long regis[5];
                regis[1]=mx1[u][e];regis[2]=mx2[u][e];regis[3]=k1;regis[4]=k2;
                sort(regis+1,regis+5);
                k1=regis[4];
                for (long long i=3;i>=1;i--)
                {
                    if (regis[i]==regis[i+1]) continue;
                    else {k2=regis[i];break;}
                }
                regis[1]=mx1[v][e];regis[2]=mx2[v][e];regis[3]=k3;regis[4]=k4;
                sort(regis+1,regis+5);
                k3=regis[4];
                for (long long i=3;i>=1;i--)
                {
                    if (regis[i]==regis[i+1]) continue;
                    else {k4=regis[i];break;}
                }
                u=posu;v=posv;
            }
        }
        long long regis[8];
        regis[1]=k1;regis[2]=k2;regis[3]=k3;regis[4]=k4;regis[5]=mx1[u][0];regis[6]=mx1[v][0];
        sort(regis+1,regis+7);
        r1=regis[6];
        for (long long i=5;i>=1;i--)
        {
            if (regis[i]==regis[i+1]) continue;
            else {r2=regis[i];break;}
        }
    }
    int main()
    {
        scanf("%lld%lld",&n,&m);
        for (long long i=1;i<=m;i++)
        {
            scanf("%lld%lld%lld",&mp[i].u,&mp[i].v,&mp[i].w);
            mp[i].flag=0;
        }
        kruskal();
        memset(mx1,0,sizeof(mx1));
        memset(mx2,0,sizeof(mx2));
        dfs(1,1);
        get_table();
        for (long long i=1;i<=m;i++)
        {
            if (mp[i].flag) continue;
            long long u=mp[i].u,v=mp[i].v,w=mp[i].w;
            get_ans(i);
            if (r1==mp[i].w) 
            {
                if (r2==-1) continue;
                dx=min(dx,mp[i].w-r2);
            }
            else if (r1<mp[i].w) dx=min(dx,mp[i].w-r1);
        }
        printf("%lld
    ",ans+dx);
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/ziliuziliu/p/5781738.html
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