BNUOJ 7697 Information Disturbing

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cmath>
 5 #include <algorithm>
 6 #include <climits>
 7 #include <vector>
 8 #include <queue>
 9 #include <cstdlib>
10 #include <string>
11 #include <set>
12 #include <stack>
13 #define LL long long
14 #define INF 1000010
15 using namespace std;
16 const int maxn = 1001;
17 struct arc{
18     int to,w;
19     arc(int x = 0,int y = 0):to(x),w(y){}
20 };
21 vector<arc>g[maxn];
22 int n,m,dp[maxn];
23 void dfs(int u,int fa,int limit){
24     for(int i = 0; i < g[u].size(); i++){
25         if(g[u][i].to == fa) continue;
26         dfs(g[u][i].to,u,limit);
27         if(g[u][i].w <= limit)
28             dp[u] += min(dp[g[u][i].to],g[u][i].w);
29         else dp[u] += dp[g[u][i].to];
30     }
31     if(g[u].size() == 1 && g[u][0].to == fa) dp[u] = INF;
32 }
33 int main() {
34     int i,j,u,v,w,lt,rt,mid,ans;
35     while(scanf("%d %d",&n,&m),n||m){
36         for(i = 0; i <= n; i++)
37             g[i].clear();
38         for(lt = rt = 1,i = 1; i < n; i++){
39             scanf("%d %d %d",&u,&v,&w);
40             g[u].push_back(arc(v,w));
41             g[v].push_back(arc(u,w));
42             if(w > rt) rt = w;
43         }
44         ans = -1;
45         while(lt <= rt){
46             mid = (lt+rt)>>1;
47             memset(dp,0,sizeof(dp));
48             dfs(1,-1,mid);
49             if(dp[1] <= m){
50                 ans = mid;
51                 rt = mid-1;
52             }else lt = mid+1;
53         }
54         printf("%d\n",ans);
55     }
56     return 0;
57 }