我nm时间复杂度竟然卡过去了

#include <bits/stdc++.h>
#define ll long long
#define pa pair<int,int>
using namespace std;
const int N=3e5+3;
int head[N];
int n,m,cnt=1,id=0,num=0;
int dfn[N],ou[N<<1],dep[N],lg[N<<1],pos[N],fa[N],falu[N],siz[N];
int mx[N<<1][45];
pa lcc[9];
struct E{
    int to,nxt,w;
}e[N<<1];
struct bian{
    int x,y;
    int l;
}b[N],now;
void add(int u,int v,int w){
    e[++cnt].nxt=head[u];
    e[cnt].to=v;
    e[cnt].w=w;
    head[u]=cnt;
}
void dfs(int x,int f,int d,int dd){
    dep[x]=d;ou[++id]=x;fa[x]=f;falu[x]=dd;dfn[x]=++num;siz[x]=1;
    for(int i=head[x];i;i=e[i].nxt){
        int to=e[i].to;
        int w=e[i].w;
        if(to==f)continue;
        dfs(to,x,d+w,w);
        siz[x]+=siz[to];
        ou[++id]=x;
    }
}
int find(int l,int r){
	if(r<l)swap(l,r);
    int g=lg[r-l+1];
    if(dep[mx[l][g]]<dep[mx[r+1-(1<<g)][g]]){
        return mx[l][g];
    }
    return mx[r+1-(1<<g)][g];
}
int lca(int x,int y){
    return find(pos[x],pos[y]);
}
bool cmp(bian a,bian b){
    return a.l>b.l;
}
int main(){
    scanf("%d%d",&n,&m);
    lg[1]=0;
    for(int i=2;i<=2*n-1;i++){
        lg[i]=lg[i>>1]+1;
    }
    for(int i=1;i<n;i++){
        int u,v,w;
        scanf("%d%d%d",&u,&v,&w);
        add(u,v,w);
        add(v,u,w);
    }
    dfs(1,0,0,0);
    for(int i=1;i<=2*n-1;i++){
        if(pos[ou[i]])continue;
        pos[ou[i]]=i;
    }
    for(int i=1;i<=2*n-1;i++){
        mx[i][0]=ou[i];
    }
    for(int j=1;j<=lg[(n<<1)-1];j++){
        for(int i=1;i<=(n<<1)-(1<<j);i++){
            if(dep[mx[i][j-1]]<=dep[mx[i+(1<<(j-1))][j-1]]){
                mx[i][j]=mx[i][j-1];
            }
            else mx[i][j]=mx[i+(1<<(j-1))][j-1];
        }
    }
    for(int i=1;i<=m;i++){
        scanf("%d%d",&b[i].x,&b[i].y);
        b[i].l=dep[b[i].x]+dep[b[i].y]-2*dep[lca(b[i].x,b[i].y)];
    }
    sort(b+1,b+1+m,cmp);
    int f,mxx;
    // now.x=b[1].x;
    // now.y=b[1].y;
    // int f=lca(now.x,now.y);
    // int mxx=0;
    // while(now.x!=f){
    //     mxx=max(mxx,falu[now.x]);
    //     now.x=fa[now.x];
    // }
    // while(now.y!=f){
    //     mxx=max(mxx,falu[now.y]);
    //     now.y=fa[now.y];
    // }
    now.x=b[1].x;
    now.y=b[1].y;
//    																bool yyyyyyy=0;
    int ans=1e9;
    for(int i=2;i<=m;i++){
        lcc[1].second=lca(now.x,b[i].x);
        lcc[1].first=dep[lcc[1].second];

        lcc[2].second=lca(now.x,b[i].y);
        lcc[2].first=dep[lcc[2].second];

        lcc[3].second=lca(now.y,b[i].x);
        lcc[3].first=dep[lcc[3].second];

        lcc[4].second=lca(now.y,b[i].y);
        lcc[4].first=dep[lcc[4].second];

        lcc[5].second=lca(now.x,now.y);
        lcc[5].first=dep[lcc[5].second];

        lcc[6].second=lca(b[i].x,b[i].y);
        lcc[6].first=dep[lcc[6].second];
        sort(lcc+1,lcc+7,greater<pa>());
        int fff=0,fff2=0;
        int yy=lca(now.x,now.y);
        int xx=lca(b[i].x,b[i].y);
        if(dep[yy]>=dep[xx]&&(yy==lca(yy,b[i].x)||yy==lca(yy,b[i].y)))fff=1;
        if(dep[xx]>=dep[yy]&&(xx==lca(xx,now.x)||xx==lca(xx,now.y)))fff2=1;
//        if(fff!=1){
        f=lca(now.x,now.y);
            mxx=0;
            while(now.x!=f){
                mxx=max(mxx,falu[now.x]);
                now.x=fa[now.x];
            }
            while(now.y!=f){
                mxx=max(mxx,falu[now.y]);
                now.y=fa[now.y];
            }
        ans=min(ans,max(b[1].l-mxx,b[i].l));
		if(lcc[1].second==lcc[2].second||(fff!=1&&fff2!=1)){
            printf("%d\n",ans);
            return 0;
        }
        else{
            now.x=lcc[1].second;
            now.y=lcc[2].second;
        }
    }
    f=lca(now.x,now.y);
    mxx=0;
    while(now.x!=f){
        mxx=max(mxx,falu[now.x]);
        now.x=fa[now.x];
    }
    while(now.y!=f){
        mxx=max(mxx,falu[now.y]);
        now.y=fa[now.y];
    }
    ans=b[1].l-mxx;
    printf("%d\n",ans);
//    if(yyyyyyy)puts("JDJSO");
    // for(int i=1;i<=2*n-1;i++){
    //     printf("%d ",ou[i]);
    // }
    return 0;
}