delete pics to save space

1.5021.cpp

@@ -0,0 +1,87 @@
+#include<cstdio>
+#include<cstring>
+#include<vector>
+#include<set>
+#include<algorithm>
+using namespace std;
+const int maxn=50005;
+int n,m,cnt;
+vector<int> G[maxn],W[maxn];
+multiset<int> s[maxn];
+int dep[maxn];
+void DFS(int u,int d)
+{
+	dep[u]=d;
+	for(int i=0;i<G[u].size();i++)
+	{
+		int &v=G[u][i];
+		if(!dep[v]) DFS(v,d+W[u][i]);
+	}
+}
+int dfs(int u,int fa,int lim)
+{
+	s[u].clear();
+	int val=0;
+	for(int i=0;i<G[u].size();i++)
+	{
+		int v=G[u][i];
+		if(v==fa) continue;
+		val=dfs(v,u,lim)+W[u][i];
+		if(val>=lim) cnt++;
+		else s[u].insert(val);
+	}
+	int maxd=0;
+	while(!s[u].empty())
+	{
+		multiset<int>::iterator bg=s[u].begin();
+		if(s[u].size()==1) return max(maxd,*bg);
+		multiset<int>::iterator it=s[u].lower_bound(lim-*bg);
+		if(it==bg&&s[u].count(*it)==1) ++it;
+		if(it==s[u].end())
+		{
+			maxd=max(maxd,*bg);
+			s[u].erase(bg);
+		}
+		else
+		{
+			cnt++;
+			s[u].erase(it);
+			s[u].erase(s[u].begin());
+		}
+	}
+	return maxd;
+}
+inline bool check(int lim)
+{
+	cnt=0;
+	dfs(1,0,lim);
+	return cnt>=m;
+}
+int main()
+{
+#ifdef local
+	freopen("pro.in","r",stdin);
+#endif
+	scanf("%d%d",&n,&m);
+	int L=1,R,M,res=1;
+	for(int i=1;i<=n-1;i++)
+	{
+		int u,v,w; scanf("%d%d%d",&u,&v,&w);
+		G[u].push_back(v); G[v].push_back(u);
+		W[u].push_back(w); W[v].push_back(w);
+	}
+	DFS(1,1);
+	int rt=1;
+	for(int i=2;i<=n;i++) if(dep[i]>dep[rt]) rt=i;
+	memset(dep,0,sizeof(dep)); DFS(rt,1);
+	R=dep[1];
+	for(int i=2;i<=n;i++) R=max(R,dep[i]); R--;
+	while(L<=R)
+	{
+		M=(L+R)>>1;
+		if(check(M)) res=M,L=M+1;
+		else R=M-1;
+	}
+	printf("%d\n",res);
+	return 0;
+}