Trucks UVA - 12655

https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=4384

题目要求任意两点之间所有路径的中 权值最小的边最大的那条路上的最小边权值是多大

没想到求个生成树就可以 暂时还不太理解 留坑..

求完最大生成树 然后普通的链上最值查询即可

#include <bits/stdc++.h>
using namespace std;
#define N 0x3f3f3f3f

struct node1
{
    int u;
    int v;
    int w;
};

struct node2
{
    int v;
    int next;
};

struct node3
{
    int l;
    int r;
    int val;
};

node1 pre[100010];
node2 edge[40010];
node3 tree[40010];
int first[20010],val[20010],f[20010],fa[20010],deep[20010],sum[20010],son[20010],top[20010],mp1[20010],mp2[20010];
int n,m,q,num;

bool cmp(node1 n1,node1 n2)
{
    return n1.w>n2.w;
}

int getf(int p)
{
    if(f[p]==p) return p;
    else
    {
        f[p]=getf(f[p]);
        return f[p];
    }
}

bool unite(int u,int v)
{
    int fu,fv;
    fu=getf(u);
    fv=getf(v);
    if(fu!=fv)
    {
        f[fv]=fu;
        return true;
    }
    else return false;
}

void addedge(int u,int v)
{
    edge[num].v=v;
    edge[num].next=first[u];
    first[u]=num++;
}

void dfsI(int cur)
{
    int i,v;
    sum[cur]=1,son[cur]=-1;
    for(i=first[cur];i!=-1;i=edge[i].next)
    {
        v=edge[i].v;
        if(v!=fa[cur])
        {
            fa[v]=cur,deep[v]=deep[cur]+1;
            dfsI(v);
            sum[cur]+=sum[v];
            if(son[cur]==-1||sum[son[cur]]<sum[v])
            {
                son[cur]=v;
            }
        }
    }
}

void dfsII(int cur,int tp)
{
    int i,v;
    num++;
    top[cur]=tp,mp1[cur]=num,mp2[num]=cur;
    if(son[cur]==-1) return;
    dfsII(son[cur],tp);
    for(i=first[cur];i!=-1;i=edge[i].next)
    {
        v=edge[i].v;
        if(v!=fa[cur]&&v!=son[cur])
        {
            dfsII(v,v);
        }
    }
}

void pushup(int cur)
{
    tree[cur].val=min(tree[2*cur].val,tree[2*cur+1].val);
}

void build(int l,int r,int cur)
{
    int m;
    tree[cur].l=l;
    tree[cur].r=r;
    if(l==r)
    {
        tree[cur].val=val[mp2[l]];
        return;
    }
    m=(l+r)/2;
    build(l,m,2*cur);
    build(m+1,r,2*cur+1);
    pushup(cur);
}

int queryII(int pl,int pr,int cur)
{
    int res;
    if(pl<=tree[cur].l&&tree[cur].r<=pr)
    {
        return tree[cur].val;
    }
    res=N;
    if(pl<=tree[2*cur].r) res=min(res,queryII(pl,pr,2*cur));
    if(pr>=tree[2*cur+1].l) res=min(res,queryII(pl,pr,2*cur+1));
    return res;
}

int queryI(int u,int v)
{
    int res;
    res=N;
    while(top[u]!=top[v])
    {
        if(deep[top[u]]<deep[top[v]]) swap(u,v);
        res=min(res,queryII(mp1[top[u]],mp1[u],1));
        u=fa[top[u]];
    }
    if(u==v) return res;
    if(deep[u]<deep[v]) swap(u,v);
    res=min(res,queryII(mp1[son[v]],mp1[u],1));
    return res;
}

int main()
{
    int i,cnt,u,v;
    while(scanf("%d%d%d",&n,&m,&q)!=EOF)
    {
        for(i=1;i<=m;i++)
        {
            scanf("%d%d%d",&pre[i].u,&pre[i].v,&pre[i].w);
        }
        sort(pre+1,pre+m+1,cmp);
        for(i=1;i<=n;i++) f[i]=i;
        cnt=0;
        for(i=1;i<=m;i++)
        {
            if(unite(pre[i].u,pre[i].v)) pre[++cnt]=pre[i];
            if(cnt==n-1) break;
        }
        memset(first,-1,sizeof(first));
        num=0;
        for(i=1;i<=n-1;i++)
        {
            addedge(pre[i].u,pre[i].v);
            addedge(pre[i].v,pre[i].u);
        }
        fa[1]=-1,deep[1]=1;
        dfsI(1);
        for(i=1;i<=n-1;i++)
        {
            if(deep[pre[i].u]<deep[pre[i].v]) swap(pre[i].u,pre[i].v);
            val[pre[i].u]=pre[i].w;
        }
        num=0;
        dfsII(1,1);
        build(1,n,1);
        while(q--)
        {
            scanf("%d%d",&u,&v);
            printf("%d\n",queryI(u,v));
        }
    }
    return 0;
}