[BZOJ 3365] Distance Statistics

[题目链接]

https://www.lydsy.com/JudgeOnline/problem.php?id=3365

[算法]

点分治

[代码]

#include <algorithm>
#include <bitset>
#include <cctype>
#include <cerrno>
#include <clocale>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <limits>
#include <list>
#include <map>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <utility>
#include <vector>
#include <cwchar>
#include <cwctype>
#include <stack>
#include <limits.h>
using namespace std;
#define MAXN 40010

int i,n,m,k,tot,len,ans,root,u,v,w;
int head[MAXN],weight[MAXN],size[MAXN],d[MAXN],dep[MAXN];
bool visited[MAXN];
char c;

struct Edge
{
    int to,w,nxt;
} e[MAXN<<];

inline void addedge(int u,int v,int w)
{
    tot++;
    e[tot] = (Edge){v,w,head[u]};
    head[u] = tot;
}
inline void get_root(int u,int fa,int total)
{
    int i,v;
    size[u] = ;
    weight[u] = ;
    for (i = head[u]; i; i = e[i].nxt)
    {
        v = e[i].to;
        if (v != fa && !visited[v])
        {
            get_root(v,u,total);
            size[u] += size[v];
            weight[u] = max(weight[u],size[v]);
        }
    }
    weight[u] = max(weight[u],total-size[u]);
    if (weight[u] < weight[root]) root = u;
}
inline void dfs(int u,int fa)
{
    int i,v,w;
    d[++len] = dep[u];
    for (i = head[u]; i; i = e[i].nxt)
    {
        v = e[i].to;
        w = e[i].w;
        if (!visited[v] && v != fa)
        {
            dep[v] = dep[u] + w;
            dfs(v,u);
        }
    }
}
inline int calc(int u)
{
    int i,j;
    int ret = ;
    len = ;
    dfs(u,);
    i = ; j = len;
    sort(d+,d+len+);
    while (i < j)
    {
        if (d[i] + d[j] <= k)
        {
            ret += j - i;
            i++;
        } else j--;
    }
    return ret;
}
inline void work(int u)
{
    int i,v,w;
    dep[u] = ;
    visited[u] = true;
    ans += calc(u);
    for (i = head[u]; i; i = e[i].nxt)
    {
        v = e[i].to;
        w = e[i].w;
        if (!visited[v])
        {
            dep[v] = w;
            ans -= calc(v);
            root = ;
            get_root(v,,size[v]);
            work(root);
        }
    }
}

int main()
{

    scanf("%d%d",&n,&m);
    memset(visited,false,sizeof(visited));
    tot = ;
    for (i = ; i <= n; i++) head[i] = ;
    for (i = ; i < n; i++)
    {
        scanf("%d%d%d %c",&u,&v,&w,&c);
        addedge(u,v,w);
        addedge(v,u,w);
    }
    scanf("%d",&k);
    size[] = weight[] = n;
    root = ;
    get_root(,,);
    ans = ;
    work(root);
    printf("%d\n",ans);

    return ;
}