哪里写错了TAT，为什么会爆炸啊。

第一个样例过了，链的数据就变成负数了，loj上的大样例已经死掉了。

Code:

#include <cstdio>
#include <string>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
typedef long long ll;

const int N=3e5+2;
const ll inf=1e18+9;

int n,k,head[N],cnt;
struct date {
    ll x;int y;
    bool operator < (const date&var) const {return x==var.x?y>var.y:x<var.x;}
    date operator + (const date&var) {return (date){x+var.x,y+var.y};}
    date operator + (const ll&var) {return (date){x+var,y};}
    date operator + (const int&var) {return (date){x+var,y};}
}dp[3][N];
ll number(date var) {return var.x;}
struct Edge{int nxt,to,val;} G[N<<1];
void add(int u,int v,int w) {
    G[++cnt]=(Edge){head[u],v,w},head[u]=cnt;
    G[++cnt]=(Edge){head[v],u,w},head[v]=cnt;
}

template <typename _Tp> inline void IN(_Tp&x) {
    char ch;bool flag=0;x=0;
    while(ch=getchar(),!isdigit(ch)) if(ch=='-') flag=1;
    while(isdigit(ch)) x=x*10+ch-'0',ch=getchar();
    if(flag) x=-x;
}

void check(ll add,int u,int fa) {
    dp[0][u]=(date){0,0},
    dp[1][u]=(date){-inf,0},
    dp[2][u]=(date){add,1};
    for(int e=head[u];e;e=G[e].nxt) {
        int v=G[e].to,w=G[e].val;
        if(v==fa) continue;
        check(add,v,u);
        date num=max(dp[0][v],max(dp[1][v],dp[2][v]));

        dp[2][u]=max(dp[2][u],dp[2][u]+num);
        dp[2][u]=max(dp[2][u],dp[1][u]+w+max(dp[0][v],dp[1][v]+(date){-add,-1}));

        dp[1][u]=max(dp[1][u],dp[1][u]+num);
        dp[1][u]=max(dp[1][u],dp[0][u]+w+max(dp[1][v],dp[0][v]+(date){add,1}));

        dp[0][u]=dp[0][u]+num;
    }return;
}

ll wqs(ll sum) {
    ll l=-sum,r=sum,mid;
    date now;
    while(l<r) {
        mid=(l+r)>>1,check(mid,1,0);
        now=max(dp[0][1],max(dp[1][1],dp[2][1]));
        if(!(now.y^k)) break;
        now.y<k?l=mid:r=mid;
    }
    check(mid,1,0);
    now=max(dp[0][1],max(dp[1][1],dp[2][1]));
    return now.x-mid*k;
}

int main() {
    freopen("P4383.in","r",stdin);
    freopen("P4383.out","w",stdout);
    IN(n),IN(k);++k;
    ll sum=0;
    for(int i=1;i<n;++i) {
        int x,y,v;IN(x),IN(y),IN(v);
        add(x,y,v),sum+=abs(v);
    }
    printf("%lld\n",wqs(sum));
    return 0;
}