HDU 3586 Information Disturbing

#include<cstdio>
#include<cstring>
#include<cmath>
#include<ctime>
#include<map>
#include<vector>
#include<string>
#include<algorithm>
#include<iostream>
using namespace std;

int n,m;
const int maxn=1000+10;
struct Edge
{
    int to;
    int val;
    Edge (int u,int v){to=u;val=v;}
};
vector<Edge>tree[maxn];
bool vis[maxn];
int dp[maxn];

void init()
{
    for(int i=0;i<=n;i++) tree[i].clear();
    memset(vis,0,sizeof vis);
    memset(dp,-1,sizeof dp);
}

void read()
{
    for(int i=1;i<=n-1;i++)
    {
        int u,v,w;
        scanf("%d%d%d",&u,&v,&w);
        Edge e1(v,w); Edge e2(u,w);
        tree[u].push_back(e1);
        tree[v].push_back(e2);
    }
}

void dfs(int now,int lim)
{
    bool fail=1;
    for(int i=0;i<tree[now].size();i++)
        if(!vis[tree[now][i].to]) fail=0;

    if(fail) return;

    bool x=0;
    int sum=0;

    for(int i=0;i<tree[now].size();i++)
    {
        if(!vis[tree[now][i].to])
        {
            vis[tree[now][i].to]=1;
            dfs(tree[now][i].to,lim);

            if(dp[tree[now][i].to]!=-1)
                sum=sum+min(tree[now][i].val,dp[tree[now][i].to]);
            else
            {
                if(tree[now][i].val<=lim) sum=sum+tree[now][i].val;
                else x=1;
            }
        }
    }
    if(!x) dp[now]=sum;
}

bool work(int lim)
{
    memset(dp,-1,sizeof dp);
    memset(vis,0,sizeof vis);
    vis[1]=1;
    dfs(1,lim);
    if(dp[1]==-1||dp[1]>m) return 0;
    return 1;
}

void BinarySearch()
{
    int left=1,right=1000,mid;
    int ans;

    if(!work(2000)) ans=-1;
    else
    {
        while(left<=right)
        {
            mid=(left+right)/2;
            if(work(mid)) ans=mid,right=mid-1;
            else left=mid+1;
        }
    }
    printf("%d\n",ans);
}

int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        if(!n&&!m) break;
        init();
        read();
        BinarySearch();
    }
    return 0;
}