HDU 6060 RXD and dividing（LCA）

#include <cstdio>
#include <algorithm>
#include <list>
#include <vector>
using namespace std;
const int N=1000010;
typedef long long LL; 
LL d[N];
int f[N],lst[N],c[N],st[N],en[N],dfn,size[N],son[N];
vector<int> v[N],w[N];
namespace fastIO{
    #define BUF_SIZE 100000
    bool IOerror=0;
    inline char nc(){
        static char buf[BUF_SIZE],*p1=buf+BUF_SIZE,*pend=buf+BUF_SIZE;
        if(p1==pend){
            p1=buf;
            pend=buf+fread(buf,1,BUF_SIZE,stdin);
            if(pend==p1){
                IOerror=1;
                return -1;
            }
        }return *p1++;
    }
    inline bool blank(char ch){
        return ch==‘ ‘||ch==‘\n‘||ch==‘\r‘||ch==‘\t‘;
    }
    inline bool read(int &x){
        char ch;
        while(blank(ch=nc()));
        if(IOerror)return false;
        for(x=ch-‘0‘;(ch=nc())>=‘0‘&&ch<=‘9‘;x=x*10+ch-‘0‘);
        return true;
    }
    #undef BUF_SIZE
};
int n,m,x,y,z;
int cnt,D[N],top[N];
LL ans;
void dfs(int x){ 
    size[x]=1;
    for(int i=0;i<v[x].size();i++){
        int y=v[x][i];
        if(y==f[x])continue;
        f[y]=x; D[y]=D[x]+1; 
        dfs(y); size[x]+=size[y];
		if(size[y]>size[son[x]])son[x]=y; 
    }cnt++;
    if(cnt>m)cnt=1;
    c[x]=cnt;
}
void dfs1(int x,int y){
	if(x==-1)return;
	st[x]=++dfn; top[x]=y;
	if(son[x])dfs1(son[x],y);
	for(int i=0;i<v[x].size();i++)if(v[x][i]!=son[x]&&v[x][i]!=f[x])dfs1(v[x][i],v[x][i]);
    en[x]=dfn;
}
int lca(int x,int y){
    for(;top[x]!=top[y];x=f[top[x]])if(D[top[x]]<D[top[y]]){int z=x;x=y;y=z;}
    return D[x]<D[y]?x:y;
}
void dfs2(int x){
    int cx=c[x];
    if(lst[cx]){ 
		int y=lst[cx];
        y=lca(x,y);
        ans+=d[x]-d[y];
    }else ans+=d[x];
    lst[cx]=x;
    for(int i=0;i<v[x].size();i++){
        int y=v[x][i],z=w[x][i];
        //printf("--%d %d\n",y,z); 
        if(y==f[x])continue;
        d[y]=d[x]+z;
        dfs2(y);
    }
}
using namespace fastIO;
int main(){
    while(read(n)){
        read(m); ans=0;
        for(int i=1;i<=n;i++)v[i].clear(),w[i].clear(),lst[i]=0,son[i]=-1;
        for(int i=1;i<n;i++){
            read(x); read(y); read(z);
            v[x].push_back(y);
            v[y].push_back(x);
            w[x].push_back(z);
            w[y].push_back(z);
        }dfn=cnt=0;
        dfs(1); c[1]=0; 
        dfs1(1,1);
        dfs2(1);
        printf("%lld\n",ans);
    }return 0;
}