[BZOJ 3363] Cow Marathon

[题目链接]

         https://www.lydsy.com/JudgeOnline/problem.php?id=3363

[算法]

         树的直径

[代码]

        

#include<bits/stdc++.h>
using namespace std;
#define MAXN 100010

struct edge
{
        int to,w,nxt;
} e[MAXN << 1];

int i,n,m,u,v,w,ans,tot;
char t[10];
int head[MAXN],d[MAXN];

inline void addedge(int u,int v,int w)
{
        tot++;
        e[tot] = (edge){v,w,head[u]};
        head[u] = tot;
}
inline void dfs(int u,int fa)
{
        int i,v,w;
        for (i = head[u]; i; i = e[i].nxt)
        {
                v = e[i].to;
                w = e[i].w;
                if (v == fa) continue;
                dfs(v,u);
                ans = max(ans,d[u] + d[v] + w);
                d[u] = max(d[u],d[v] + w);
        }
}
int main() 
{
        
        scanf("%d%d",&n,&m);
        for (i = 1; i <= m; i++)
        {
                scanf("%d%d%d%s",&u,&v,&w,&t);
                addedge(u,v,w);
                addedge(v,u,w);
        }
        dfs(1,0);
        printf("%d
",ans);
        
        return 0;
    
}