广告：

#include <stdio.h>
int main()
{
    puts("转载请注明出处[vmurder]谢谢");
    puts("网址：blog.csdn.net/vmurder/article/details/44307489");
}

题意&题解

http://blog.csdn.net/vmurder/article/details/44302921

代码：（同一道题）

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define N 50100
#define inf 0x3f3f3f3f
using namespace std;
int n,m;
struct Eli
{
    int v,len,next;
}e[N<<1];
int head[N],cnt;
bool rem[N];
inline void add(int u,int v,int len)
{
    e[++cnt].v=v;
    e[cnt].len=len;
    e[cnt].next=head[u];
    head[u]=cnt;
}
int f[N],f2[N],son[N];
int TreeCenter,length;
int dfs1(int x,int p)
{
    int i,v;
    f[x]=f2[x]=0;
    for(i=head[x];i;i=e[i].next)
    {
        v=e[i].v;
        if(v==p||rem[v])continue;
        int temp=dfs1(v,x);
        if(temp>f[x])
        {
            f2[x]=f[x];
            f[x]=temp;
            son[x]=v;
        }
        else if(temp>f2[x])
            f2[x]=temp;
    }
    return f[x]+1;
}
int g[N];
void dfs2(int x,int p)
{
    int i,v;
    if(max(f[x],g[x])<length)
    {
        length=max(f[x],g[x]);
        TreeCenter=x;
    }
    for(i=head[x];i;i=e[i].next)
    {
        v=e[i].v;
        if(v==p||rem[v])continue;
        if(v==son[x])g[v]=max(g[x],f2[x])+1;
        else g[v]=max(g[x],f[x])+1;
        dfs2(v,x);
    }
    return ;
}
inline int get_TreeCenter(int x)
{
    if(rem[x])return 0;
    length=inf,g[x]=0;
    dfs1(x,0),dfs2(x,0);
    return TreeCenter;
}
struct Summorer
{
    int a,b;
    // 权值，子树标号
    Summorer(int _a=0,int _b=0):a(_a),b(_b){}
}src[N];
inline int cmpa(Summorer a,Summorer b)
{
    return a.a<b.a;
}
inline int cmpb(Summorer a,Summorer b)
{
    return a.b==b.b?a.a<b.a:a.b<b.b;
}
int size[N];
void dfs3(int x,int p,int t,int len)
{
    src[++cnt]=Summorer(len,t);
    size[x]=1;
    int i,v;
    for(i=head[x];i;i=e[i].next)
    {
        v=e[i].v;
        if(rem[v]||v==p)continue;
        dfs3(v,x,t,len+e[i].len);
        size[x]+=size[v];
    }
    return ;
}
int ans;
void work(int x,int n)
{
    if(!n)return ;
    rem[x=get_TreeCenter(x)]=1;
    int num=0,i,j,k,v,p;
    cnt=0;
    for(i=head[x];i;i=e[i].next)
    {
        v=e[i].v;
        if(rem[v])continue;
        dfs3(v,x,++num,e[i].len);
    }
    sort(src+1,src+cnt+1,cmpa);
    p=n;
    for(i=0;i<=n;i++)
    {
        while(i<p&&src[i].a+src[p].a>m)p--;
        if(i>=p)break;
        ans+=(p-i);
    }
    sort(src+1,src+cnt+1,cmpb);
    src[cnt+1].b=-1;
    for(i=0;i<=n;i=j)
    {
        for(j=i+1;src[j].b==src[i].b;j++);
        for(p=j-1,k=i;k<j;k++)
        {
            while(k<p&&src[k].a+src[p].a>m)p--;
            if(k>=p)break;
            ans-=(p-k);
        }
    }
    for(i=head[x];i;i=e[i].next)
    {
        v=e[i].v;
        if(rem[v])continue;
        work(v,size[v]-1);
    }
    return ;
}
void init()
{
    ans=cnt=0;
    memset(rem,0,sizeof rem);
    memset(head,0,sizeof head);
}
char useless[5];
int main()
{
    freopen("test.in","r",stdin);
    int i,a,b,c;

    while(scanf("%d%d",&n,&m)!=EOF)
    {
        init();
        while(m--)
        {
            scanf("%d%d%d%s",&a,&b,&c,useless);
            add(a,b,c),add(b,a,c);
        }
        scanf("%d",&m);
        work(1,n-1);
        printf("%d\n",ans);
    }

    return 0;
}