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| #include <bits/stdc++.h>
using namespace std;
struct bbbb
{
int to, nextt, xx;
} b[10010];
int n, tail, dd[5010], dis[5010], vis[5010], ldd, rdd, diss[5010], ttll;
struct llbb
{
int xxx, x;
} lb[5010];
struct cccc
{
int zjcd, bjcd, zd;
} cc1[5010], cc2[5010];
void jb(int x, int y, int z)
{
tail++;
b[tail].nextt = dd[x];
b[tail].to = y;
b[tail].xx = z;
dd[x] = tail;
return;
}
queue<int> q;
void bfs(int x)
{
memset(vis, 0, sizeof(vis));
dis[x] = 0;
vis[x] = 1;
q.push(x);
while (q.empty() == false)
{
int xx = q.front();
q.pop();
for (int i = dd[xx]; i != 0; i = b[i].nextt)
{
if (vis[b[i].to] == 0)
{
vis[b[i].to] = 1;
dis[b[i].to] = dis[xx] + b[i].xx;
q.push(b[i].to);
}
}
}
return;
}
bool dfs(int x, int mb)
{
if (x == mb)
{
ttll++;
lb[ttll].x = x;
return true;
}
for (int i = dd[x]; i != 0; i = b[i].nextt)
{
if (vis[b[i].to] == 0)
{
vis[b[i].to] = 1;
if (dfs(b[i].to, mb) == true)
{
ttll++;
lb[ttll].x = x;
lb[ttll].xxx = b[i].xx;
return true;
}
}
}
return false;
}
int bfs1(int x)
{
int maxx = 0;
q.push(x);
while (q.empty() == false)
{
int xx = q.front();
q.pop();
maxx = max(maxx, diss[xx]);
for (int i = dd[xx]; i != 0; i = b[i].nextt)
{
if (vis[b[i].to] == 0)
{
vis[b[i].to] = 1;
diss[b[i].to] = diss[xx] + b[i].xx;
q.push(b[i].to);
}
}
}
return maxx;
}
int main()
{
scanf("%d", &n);
for (int i = 1; i < n; i++)
{
int x, y, z;
scanf("%d%d%d", &x, &y, &z);
jb(x, y, z);
jb(y, x, z);
}
bfs(1);
for (int i = 1; i <= n; i++)
{
if (dis[ldd] <= dis[i])
{
ldd = i;
}
}
bfs(ldd);
for (int i = 1; i <= n; i++)
{
if (dis[rdd] <= dis[i])
{
rdd = i;
}
}
memset(vis, 0, sizeof(vis));
vis[ldd] = 1;
dfs(ldd, rdd);
memset(vis, 0, sizeof(vis));
for (int i = 1; i <= ttll; i++)
{
vis[lb[i].x] = 1;
}
int zhongd = 1;
for (int i = 2; i <= ttll; i++)
{
diss[lb[i].x] = diss[lb[i - 1].x] + lb[i].xxx;
int qwq = bfs1(lb[i].x);
if (qwq <= cc1[lb[i - 1].x].zjcd)
{
cc1[lb[i].x] = cc1[lb[i - 1].x];
}
else
{
while (zhongd < i && max(diss[lb[zhongd].x], qwq - diss[lb[zhongd].x]) > max(diss[lb[zhongd + 1].x], qwq - diss[lb[zhongd + 1].x]))
{
zhongd++;
}
cc1[lb[i].x].zjcd = qwq;
cc1[lb[i].x].bjcd = max(diss[lb[zhongd].x], qwq - diss[lb[zhongd].x]);
}
}
memset(vis, 0, sizeof(vis));
memset(diss, 0, sizeof(diss));
for (int i = 1; i <= ttll; i++)
{
vis[lb[i].x] = 1;
}
zhongd = ttll;
for (int i = ttll - 1; i >= 1; i--)
{
diss[lb[i].x] = diss[lb[i + 1].x] + lb[i + 1].xxx;
int qwq = bfs1(lb[i].x);
if (qwq <= cc2[lb[i + 1].x].zjcd)
{
cc2[lb[i].x] = cc2[lb[i + 1].x];
}
else
{
while (zhongd > i && max(diss[lb[zhongd].x], qwq - diss[lb[zhongd].x]) > max(diss[lb[zhongd - 1].x], qwq - diss[lb[zhongd - 1].x]))
{
zhongd--;
}
cc2[lb[i].x].zjcd = qwq;
cc2[lb[i].x].bjcd = max(diss[lb[zhongd].x], qwq - diss[lb[zhongd].x]);
}
}
int minn = 1e9;
for (int i = 1; i < ttll; i++)
{
minn = min(minn, max(cc1[lb[i].x].bjcd + cc2[lb[i + 1].x].bjcd + lb[i + 1].xxx, max(cc1[lb[i].x].zjcd, cc2[lb[i + 1].x].zjcd)));
}
printf("%d", minn);
return 0;
}
|