hdu 4607 Park Visit

求树的直径

#include <stdio.h>
#include <string.h>
const int MAXN = 100010;
struct node
{
int to, next;
}data[MAXN*2];
int head[MAXN], n, m, sz;
void add(int u, int v)
{
data[sz].to = v;
data[sz].next = head[u];
head[u] = sz++;
data[sz].to = u;
data[sz].next = head[v];
head[v] = sz++;
}
int fnum[MAXN], snum[MAXN], cnt[MAXN];
void dfs(int u, int pre)
{
int v, i;
fnum[u] = snum[u] = 0;
for (i = head[u]; ~i; i=data[i].next)
{
if ( (v=data[i].to) == pre) continue;
dfs(v, u);
if (fnum[v]+1 > fnum[u])
{
snum[u] = fnum[u];
fnum[u] = fnum[v]+1;
}
else if (fnum[v]+1 > snum[u])
{
snum[u] = fnum[v]+1;
}
}
i = head[u];
if (u != 1)
if (i == -1 || data[i].next == -1) /// leaf node
{
fnum[u]=snum[u] = 0;
cnt[u] = 0;
return;
}
int c1=0, c2=0;
for (i = head[u]; ~i; i=data[i].next)
{
if ( (v=data[i].to) == pre) continue;
if (fnum[u] == fnum[v]+1) c1++;
else if (snum[u] == fnum[v]+1) c2++;
}
if (c1 >= 2)
{
cnt[u] = fnum[u]*2;
}
else if (c1 >= 1 && c2 >= 1)
{
cnt[u] = fnum[u]+snum[u];
}
else
cnt[u] = fnum[u];
}
int main()
{
#ifndef ONLINE_JUDGE
freopen("in.txt", "r", stdin);
#endif // ONLINE_JUDGE
int t;
scanf("%d", &t);
while (t--)
{
scanf("%d%d", &n, &m);
sz = 0;
memset(head, -1, sizeof head);
for (int i = 1; i< n; i++)
{
int u, v;
scanf("%d%d", &u, &v);
add(u, v);
}
dfs(1, -1);
int mx = 0;
for (int i = 1; i<= n; ++i)
{
if (cnt[i] > mx) mx=cnt[i];
}
++mx;
for (int i = 0; i< m; ++i)
{
scanf("%d", &sz);
if (sz <= mx)
printf("%d\n", sz-1);
else
printf("%d\n", mx-1+(sz-mx)*2);
}
}
return 0;
}