hrbust 1750 Eternal Victory(树+广搜 类似找树的直径...)

从1点出发每个点都走到 求最少要走多少 权值和*2-最长路就是答案   

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdio>
#define MAXN 211115
#define MAXM 211111
#define INF 0x1f1f1f1f
using namespace std;
int n, m;
struct EDGE
{
int v, next;
int w;
}edge[MAXN];
int head[MAXN], e;
int q[MAXN], vis[MAXN];
long long d[MAXN];
void init()
{
e = 0;
memset(head, -1, sizeof(head));
}
void add(int u, int v, int w)
{
edge[e].v = v;
edge[e].w = w;
edge[e].next = head[u];
head[u] = e++;
}
void bfs(int src)
{
for(int i = 1; i <= n; i++) {vis[i] = 0, d[i] = INF;}
int h = 0, t = 0;
q[t++] = src;
vis[src] = 1;
d[src] = 0;
while(h < t)
{
int u = q[h++];
for(int i = head[u]; i != -1; i = edge[i].next)
{
int v = edge[i].v;
int w = edge[i].w;
if(d[u] + w < d[v])
{
d[v] = d[u] + w;
if(!vis[v])
{
q[t++] = v;
vis[v] = 1;
}
}
}
}
}
int main()
{
int u, v, w;
long long sum;
while(scanf("%d", &n)!=EOF)
{
sum=0;
init();
for(int i = 1; i <= n-1; i++)
{
scanf("%d%d%d", &u, &v, &w);
add(u, v, w);
add(v, u, w);
sum=sum+w;
}
bfs(1);
int pos = -1;
long long mx = -1;
for(int i = 1; i <= n; i++)
if(d[i] > mx&&d[i]<INF)
// if(d[i] > mx)
{
mx = d[i];
pos = i;
}
printf("%lld\n", sum*2-mx);
}
return 0;
}