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zc
2019-12-21 19:47:00
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  1. b_i = a_i + 1

    一条链

    直接二分最小值,然后判断即可

  2. m=1

    直接找树的直径

  3. a_i = 1

    记录所有边权,设边权为w,然后排序

    w_1 + w_{2m} , w_2 + w_{2m-1}, ...的最小值

  4. 分支不超过3(基本上就是正解了)

明摆着就是正解嘛

dfs(x,f,w)求出x的子树连接x长度不超过w的最长路径

路径分为两种

一种\ge w,那直接条数++

另一种a+b \ge w

那我们直接用multiset存,每次lowerbound找到最接近的,然后返回

stl,还是太弱了Q\omega Q

#include<bits/stdc++.h>
namespace ZDY{
    #pragma GCC optimize(3)
    #define il __inline__ __attribute__ ((always_inline))
    #define rg register
    #define ll long long
    #define ull unsigned long long
    #define db double
    #define sht short
    #define MB template <class T>il
    #define Fur(i,x,y) for(int i=x;i<=y;i++)
    #define Fdr(i,x,y) for(int i=x;i>=y;i--)
    #define fl(i,x) for(int i=head[x],to;to=e[i].to,i;i=e[i].nxt)
    #define clr(x,y) memset(x,y,sizeof(x))
    #define cpy(x,y) memcpy(x,y,sizeof(x))
    #define fin(s) freopen(s".in","r",stdin)
    #define fout(s) freopen(s".out","w",stdout)
    #define fcin ios::sync_with_stdio(false)
    #define l2(n) (int(log2(n)))
    #define inf 0x3f3f3f3f
    MB T ABS(T x){return x>0?x:-x;}
    MB T MAX(T x,T y){return x>y?x:y;}
    MB T MIN(T x,T y){return x<y?x:y;}
    MB T GCD(T x,T y){return y?GCD(y,x%y):x;}
    MB void SWAP(T &x,T &y){T t=x;x=y;y=t;}
}using namespace ZDY;using namespace std;
namespace IO{const char* ln="\n";const int str=1<<20;struct IN{char buf[str],*s,*t;bool _;IN():s(buf),t(buf),_(0){}il char gc(){return s==t&&((t=(s=buf)+fread(buf,1,str,stdin))==s)?EOF:(*s++);}IN&operator>>(char&ch){if(_)return *this;char c;while((c=gc())!=EOF&&isspace(c));if(c==EOF)_=1;else ch=c;return *this;}IN& operator>>(char* ch){if(_)return *this;char c;while((c=gc())!=EOF&&isspace(c));if(c==EOF)return _=1,*this;*ch=c;ch++;while((c=gc())!=EOF&&!isspace(c))*ch=c,ch++;if(c==EOF)_=1;return *this;}IN& operator>>(string& ch){if(_)return *this;char c;while((c=gc())!=EOF&&isspace(c));if(c==EOF)return _=1,*this;ch+=c;while((c=gc())!=EOF&&!isspace(c))ch+=c;if(c==EOF)_=1;return *this;}template<typename T>IN&operator>>(T&x){if(_)return *this;char c=gc();bool ff=0;while(c!=EOF&&(c<'0'||c>'9'))ff^=(c=='-'),c=gc();if(c==EOF){_=1;return *this;}x=0;while(c!=EOF&&'0'<=c&&c<='9')x=(x<<3)+(x<<1)+c-48,c=gc();if(c==EOF)_=1;if(ff)x=-x;return *this;}}in;struct OUT{char buf[str],*s,*t;OUT():s(buf),t(buf+str){}~OUT(){fwrite(buf,1,s-buf,stdout);}void pt(char c){(s==t)?(fwrite(s=buf,1,str,stdout),*s++=c):(*s++=c);}OUT&operator<<(const char*s){while(*s)pt(*s++);return *this;}OUT&operator<<(char*s){while(*s)pt(*s++);return *this;}OUT&operator<<(string s){for(int i=0;s[i];i++)pt(s[i]);return *this;}template<typename T>OUT&operator<<(T x){if(!x)return pt('0'),*this;if(x<0)pt('-'),x=-x;char a[30],t=0;while(x)a[t++]=x%10,x/=10;while(t--)pt(a[t]+'0');return *this;}}out;}using namespace IO;
#define N 50011
int n,m,head[N],cnt=0,ans;
multiset<int>s[N];
struct edge{
    int to,nxt,w;
}e[N*2];
void add(int x,int y,int w){
    e[++cnt].to=y;e[cnt].nxt=head[x];e[cnt].w=w;head[x]=cnt;
}
int dfs(int x,int f,int w){
    s[x].clear();
    int v;
    fl(i,x)if(to!=f){
        v=dfs(to,x,w)+e[i].w;
        if(v>=w)ans++;
        else s[x].insert(v);
    }
    multiset<int>::iterator it;
    v=0;
    while(!s[x].empty()){
        int t=*s[x].begin();
        if(s[x].size()==1)return MAX(v,t);
        it=s[x].lower_bound(w-t);
        if(it==s[x].begin()&&s[x].count(*it))it++;
        if(it==s[x].end())v=MAX(v,t),s[x].erase(s[x].begin());
        else{
            ans++;
            s[x].erase(s[x].begin());
            s[x].erase(it);
        }
    }
    return v;
}
bool chk(int w){
    ans=0;
    dfs(1,0,w);
    return ans>=m;
}
int main(){
    in>>n>>m;
    int x,y,w;
    Fur(i,1,n-1)in>>x>>y>>w,add(x,y,w),add(y,x,w);
    int l=0,r=1<<30,mid,as=0;
    while(l<=r){
        mid=(l+r)>>1;
        if(chk(mid))as=mid,l=mid+1;
        else r=mid-1;
    }
    out<<as<<ln;
}
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