This problem k orders of magnitude 1000000, so I did not dare to open a million local array.
Why global likely to go wrong? Because the recursive time, this data may be one of the next layer use.
How to avoid them is to separate processing and recursion. Get away!
Look at the code:
#include<bits/stdc++.h>
using namespace std;
const int maxn=1000000+100;
#define inf 1e9
int n,k;
int beg[maxn],nex[maxn],to[maxn],w[maxn],e;
void add(int x,int y,int z){
e++;nex[e]=beg[x]; beg[x]=e;to[e]=y;w[e]=z; } int mx,rt,size; int sz[maxn],son[maxn],vis[maxn]; inline void getrt(int x,int fa){ sz[x]=1,son[x]=0; for(int i=beg[x];i;i=nex[i]){ int t=to[i]; if(t==fa||vis[t])continue; getrt(t,x); sz[x]+=sz[t]; if(son[x]<sz[t])son[x]=sz[t]; } if(son[x]<size-sz[x])son[x]=size-sz[x]; if(son[x]<mx)mx=son[x],rt=x; } int bot[maxn],top,q1[maxn],q2[maxn],ans; inline void stk(int x,int fa,int val,int edge){ if(val>k)return; if(val==k){ ans=min(ans,edge); return; } if(edge>=ans)return; q1[++top]=val; q2[top]=edge; for(int i=beg[x];i;i=nex[i]){ int t=to[i]; if(t==fa||vis[t])continue; stk(t,x,val+w[i],edge+1); } } int tmp[maxn],qwq; inline void divide(int x){ vis[x]=1;qwq=0; for(int i=beg[x];i;i=nex[i]){ int t=to[i]; if(vis[t])continue; top=0; stk(t,x,w[i],1); for(int j=1;j<=top;j++) ans=min(ans,q2[j]+bot[k-q1[j]]); for(int j=1;j<=top;j++) bot[q1[j]]=min(bot[q1[j]],q2[j]); for(int j=1;j<=top;j++) tmp[++qwq]=q1[j]; } for(int i=1;i<=qwq;i++) bot[tmp[i]]=inf; for(int i=beg[x];i;i=nex[i]){ int t=to[i]; if(vis[t])continue; mx=inf,rt=0,size=sz[t]; getrt(t,x); divide(rt); } } int main(){ cin>>n>>k; int x,y,z; for(int i=1;i<n;i++){ scanf("%d%d%d",&x,&y,&z); x++,y++; add(x,y,z),add(y,x,z); } for(int i=1;i<=k;i++) bot[i]=1e9; ans=inf; mx=inf,rt=0,size=n; getrt(1,0); divide(rt); if(ans>=n)puts("-1"); else printf("%d\n",ans); return 0; }
Unfortunately, I was again the AC, ha ha ha!