BZOJ 3124 直径

Posted 2020-08-09 ziliuziliu

计算去掉每一条边之后的直径。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxv 200500
#define maxe 400500
using namespace std;
struct edge
{
    long long v,w,mx,nxt;
}e[maxe];
int t,n,x,y,z,g[maxv],nume=1,root;
int fath_e[maxv],son[maxv],pos;
long long val1[maxv],val2[maxv],ans=0,dis[maxv],ret=0,dr=0;
inline int read()
{
    int data=0;char ch;
    while (ch<‘0‘ || ch>‘9‘)
        ch=getchar();
    while (ch>=‘0‘ && ch<=‘9‘)
    {
        data=data*10+ch-‘0‘;
        ch=getchar();
    }
    return data;
}
inline void reset1()
{
    memset(g+1,0,n*sizeof(int));
    ans=0;nume=1;ret=0;
}
inline void reset2()
{
    memset(son+1,0,n*sizeof(int));
}
inline void addedge(int u,int v,int w)
{
    e[++nume].v=v;
    e[nume].w=w;
    e[nume].mx=0;
    e[nume].nxt=g[u];
    g[u]=nume;
}
void dfs1(int x,int fath)
{
    for (int i=g[x];i;i=e[i].nxt)
    {
        int v=e[i].v;
        if (v!=fath)
        {
            dis[v]=dis[x]+e[i].w;
            if (dis[v]>ret) {ret=dis[v];root=v;}
            dfs1(v,x);
        }
    }
}
void dfs2(int x,int fath)
{
    val1[x]=val2[x]=0;long long fx=0,sx=0;
    for (int i=g[x];i;i=e[i].nxt)
    {
        int v=e[i].v;
        if (v!=fath)
        {
            dis[v]=dis[x]+e[i].w;fath_e[v]=i;
            dfs2(v,x);
            if (val2[v]+e[i].w>fx) {sx=fx;fx=val2[v]+e[i].w;son[x]=v;}
            else if (val2[v]+e[i].w>sx) sx=val2[v]+e[i].w;
            val1[x]=max(val1[x],val1[v]);
        }
    }
    val2[x]=fx;
    val1[x]=max(val1[x],fx+sx);
}
inline void get_labled(int type)
{
    int now=son[root];long long regis=0;
    while (now)
    {
        e[fath_e[now]].mx=max(e[fath_e[now]].mx,val1[now]);
        e[fath_e[now]^1].mx=max(e[fath_e[now]^1].mx,val1[now]);
        if (type==2) 
            if (e[fath_e[now]].mx!=dr) 
                ans++;
        ret++;pos=now;now=son[now];
    }
}
inline void work()
{
    reset1();
    n=read();
    for (register int i=1;i<=n-1;i++)
    {
        x=read();y=read();z=read();
        addedge(x,y,z);addedge(y,x,z);
    }
    ret=0;
    dfs1(1,1);
    reset2();dis[root]=0;fath_e[root]=0;
    dfs2(root,root);
    ret=0;dr=val1[root];
    get_labled(1);
    reset2();root=pos;dis[root]=0;fath_e[root]=0;
    dfs2(root,root);
    get_labled(2);
    printf("%lld\n%lld\n",dr,ans);
}
int main()
{
    work();
    return 0;
}