HDU 4679 Terrorist’s destroy

如果不在最长路的边，那么肯定是w*最长路。

如果在最长路，那么把最长路分成两段，左边树的最长路就是左段+左边点的次短路(不包含最长路上的点的最长路) ，右边同理。

还有就是更新，经过左端点的最长路，不一定是整颗左边树的最长路，乱搞一下就可以了。我是搞成一条链，写的很麻烦。。从一点搞到了快四点。。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <queue>
#include <algorithm>
using namespace std;
#define INF 1000000
struct node
{
    int u,v,w,next,id;
} edge[200000];
int t,n,first[200001],flag[200001];
int d[100001],in[100001],pre[100001];
int pre1[100001];
int pre2[100001];
int sp1[100001];
int sp2[100001];
int sp3[100001];
int sp4[100001];
int dp[200001];
int qu[100001];
int qv[100001];
int qw[100001];
void CL()
{
    int i;
    for(i = 0; i <= n; i ++)
    {
        first[i] = -1;
        flag[i] = 0;
        dp[i] = 0;
    }
    t = 1;
}
void add(int u,int v,int w,int id)
{
    edge[t].u = u;
    edge[t].v = v;
    edge[t].w = w;
    edge[t].next = first[u];
    edge[t].id = id;
    first[u] = t ++;
}
void dfs(int x)
{
    int i,maxz,v;
    in[x] = 1;
    maxz = 0;
    for(i = first[x]; i != -1; i = edge[i].next)
    {
        v = edge[i].v;
        if(flag[v]||in[v]) continue;
        in[v] = 1;
        dfs(v);
        maxz =  dp[v] + 1;
    }
    dp[x] = maxz;
    return;
}
int spfa(int x)
{
    int u,v,i;
    for(i = 1; i <= n; i ++)
    {
        d[i] = -INF;
        pre[i] = -1;
        in[i] = 0;
    }
    queue<int>que;
    que.push(x);
    in[x] = 1;
    d[x] = 0;
    while(!que.empty())
    {
        u = que.front();
        que.pop();
        for(i = first[u]; i != -1; i = edge[i].next)
        {
            v = edge[i].v;
            if(in[v]) continue;
            if(d[v] < d[u] + 1)
            {
                d[v] = d[u] + 1;
                pre[v] = u;
                pre1[v] = i;
                in[v] = 1;
                que.push(v);
            }
        }
    }
    int id,maxz = 0;
    for(i = 1; i <= n; i ++)
    {
        if(maxz < d[i])
        {
            maxz = d[i];
            id = i;
        }
    }
    return id;
}
int main()
{
    int cas,i,u,v,w,a,b,tmax,bb,aa,sn = 1;
    scanf("%d",&cas);
    while(cas--)
    {
        scanf("%d",&n);
        CL();
        for(i = 1; i < n; i ++)
        {
            scanf("%d%d%d",&u,&v,&w);
            add(u,v,w,i);
            add(v,u,w,i);
            qu[i] = u;
            qv[i] = v;
            qw[i] = w;
        }
        b = spfa(a = spfa(1));
        bb = b;
        aa = a;
        tmax = d[b];
        while(b != a)
        {
            flag[b] = 1;
            pre2[pre[b]] = b;
            b = pre[b];
        }
        flag[a] = 1;
        for(i = 1; i <= n; i ++)
            in[i] = 0;
        for(i = 1; i <= n; i ++)
        {
            if(flag[i]||in[i])
            {
                dfs(i);
            }
        }
        int minz = INF,num,res = -1;
        b = bb;
        num = 0;
        while(1)
        {
            sp1[b] = dp[b]+tmax - num;
            sp2[b] = num + dp[b];
            num ++;
            if(a == b) break;
            b = pre[b];
        }
        int pos = 0;
        b = bb;
        a = aa;
        while(b != a)
        {
            sp2[pre[b]] = max(pos,sp2[pre[b]]);
            pos = sp2[pre[b]];
            b = pre[b];
        }
        b = bb;
        a = aa;
        pos = 0;
        while(a != b)
        {
            sp1[pre2[a]] = max(pos,sp1[pre2[a]]);
            pos = sp1[pre2[a]];
            a = pre2[a];
        }
        b = bb;
        a = aa;
        for(i = 1; i < n; i ++)
        {
            if(flag[qu[i]]&&flag[qv[i]])
            {
                if(pre[qu[i]] == qv[i])
                {
                    u = qu[i];
                    v = qv[i];
                }
                else
                {
                    u = qv[i];
                    v = qu[i];
                }
                int tt = qw[i]*(max(sp1[v],sp2[u]));
                if(minz > tt)
                {
                    minz = tt;
                    res = i;
                }
                else if(minz == tt)
                {
                    res = min(res,i);
                }
            }
            else
            {
                if(minz > qw[i]*tmax)
                {
                    minz = qw[i]*tmax;
                    res = i;
                }
                else if(minz == qw[i]*tmax)
                {
                    res = min(res,i);
                }
            }
        }
        printf("Case #%d: %d
",sn++,res);
    }
    return 0;
}