LYDSY 1912
题目大意
暂无
题目解法
暂无
RTFC
#include <cstdio>
#include <cstring>
int n, k, head[100010], next[100010 << 1], from[100010 << 1], to[100010 << 1], len[100010 << 1],
maxlen, ecnt, fa[100010], mx1[100010], mx2[100010], en;
void addEdge(int f, int t)
{
next[ecnt] = head[f];
head[f] = ecnt;
to[ecnt] = t;
from[ecnt] = f;
len[ecnt] = 1;
ecnt++;
}
int dfs(int u, int fa)
{
int max1 = 0, max2 = 0;
for (int i = head[u]; ~i; i = next[i])
if (to[i] != fa)
{
int tmp = len[i] + dfs(to[i], u);
if (tmp > max1)
{
max2 = max1;
max1 = tmp;
mx2[u] = mx1[u];
mx1[u] = i;
}
else if (tmp > max2)
{
max2 = tmp;
mx2[u] = i;
}
}
if (maxlen < max1 + max2) maxlen = max1 + max2, en = u;
return max1;
}
int main()
{
memset(head, -1, sizeof(head));
scanf("%d%d", &n, &k);
for (int i = 1, x, y; i < n; i++)
{
scanf("%d%d", &x, &y);
addEdge(x, y);
addEdge(y, x);
}
dfs(1, 0);
int ans = ((n - 1) << 1) - (maxlen - 1);
if (k == 2)
{
for (int i = mx1[en]; i; i = mx1[to[i]]) len[i] = len[i ^ 1] = -1;
for (int i = mx2[en]; i; i = mx1[to[i]]) len[i] = len[i ^ 1] = -1;
maxlen = 0;
dfs(1, 0);
ans -= maxlen - 1;
}
printf("%d", ans);
return 0;
}