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| #include<bits/stdc++.h>
using namespace std;
const int N = 5e4 + 5;
int n, m, mid, cnt, tot, head[N];
struct E {
int nxt, v, w;
}e[N << 1];
void add(int a, int b, int c) {
e[++tot] = E{head[a], b, c}; head[a] = tot;
e[++tot] = E{head[b], a, c}; head[b] = tot;
}
#define IT multiset<int>::iterator
int dfs(int u, int fa) {
multiset<int> s;
for (int i = head[u]; i; i = e[i].nxt) {
int v = e[i].v, w = e[i].w;
if (v == fa) continue;
int d = dfs(v, u) + w;
if (d >= mid) cnt++;
else s.insert(d);
}
int mx = 0;
while (!s.empty()) {
IT it = s.begin();
int x = *it;
s.erase(it);
IT t = s.lower_bound(mid - x);
if (t == s.end()) mx = x;
else s.erase(t), cnt++;
}
return mx;
}
int main() {
freopen("track.in", "r", stdin);
freopen("track.out", "w", stdout);
int l = 0, r = 0, ans = 0;
scanf("%d %d", &n, &m);
for (int i = 1; i < n; i++) {
int u, v, w;
scanf("%d %d %d", &u, &v, &w);
add(u, v, w);
l = min(l, w); r += w;
}
while (l <= r) {
mid = (l + r) >> 1;
cnt = 0;
dfs(1, 0);
if (cnt >= m) l = mid + 1, ans = mid;
else r = mid - 1;
}
printf("%d\n", ans);
return 0;
}
|