树的直径,两遍bfs实现。
#include <cstdio>
#include <cstring>
const int MAXN = 10010;
struct Edge
{
int v, w, next;
}edge[MAXN * 2];
int edgeNumber, head[MAXN];
int destination, distance;
inline void addEdge(int u, int v, int w)
{
edge[edgeNumber].v = v;
edge[edgeNumber].w = w;
edge[edgeNumber].next = head[u];
head[u] = edgeNumber ++;
}
int dist[MAXN];
int queue[MAXN];
int front, rear;
bool visit[MAXN];
void bfs(int start)
{
memset(visit, false, sizeof(visit));
memset(dist, -1, sizeof(dist));
queue[0] = start;
visit[start] = true;
dist[start] = 0;
front = 0, rear = 1;
while(front < rear)
{
int u = queue[front++];
for(int i=head[u];i!=-1;i=edge[i].next)
{
int v = edge[i].v;
int w = edge[i].w;
if(dist[v] == -1 || dist[v] > dist[u] + w)
{
dist[v] = dist[u] + w;
if(!visit[v])
{
visit[v] = true;
queue[rear++] = v;
}
}
}
}
destination = 1;
distance = 0;
for(int i=0;i<MAXN;++i)
{
if(dist[i] > distance)
{
distance = dist[i];
destination = i;
}
}
}
int main()
{
int u, v, w;
edgeNumber = 0;
memset(head, -1, sizeof(head));
while(~scanf("%d%d%d",&u,&v,&w))
{
addEdge(u, v, w);
addEdge(v, u, w);
}
bfs(1);
bfs(destination);
printf("%d\n", distance);
return 0;
}