[BZOJ4876][ZJOI2017]线段树

没有用到任何算法，代码只有60+行，但是细节多如牛毛，各种分类讨论必须全部想清楚才行。

https://www.cnblogs.com/xiejiadong/p/6811289.html

 #include<cstdio>
 #include<algorithm>
 #define rep(i,l,r) for (int i=l; i<=r; i++)
 typedef long long ll;
 using namespace std;

 const int N=;
 ll n,nd,tot,m,u,l,r,S,mid[N],ls[N],rs[N],sm[N][],dep[N],sd[N][],fa[N][],L[N],R[N],pos[N];

 bool bel(int x,int y){ return L[x]>=L[y] && R[x]<=R[y]; }
 ll lca(ll a,ll b){
     if (bel(a,b)) return b;
     if (bel(b,a)) return a;
     ll now=a;
     for (ll i=S; ~i; i--) if (fa[now][i] && !bel(b,fa[now][i])) now=fa[now][i];
     return fa[now][];
 }

 void Dfs(ll x){
     if (!ls[x]) return;
     sm[rs[x]][]=sm[x][]; sm[rs[x]][]=sm[x][]+;
     sm[ls[x]][]=sm[x][]+; sm[ls[x]][]=sm[x][];
     dep[ls[x]]=dep[rs[x]]=dep[x]+;
     sd[rs[x]][]=sd[x][]; sd[rs[x]][]=sd[x][]+dep[x]+;
     sd[ls[x]][]=sd[x][]+dep[x]+; sd[ls[x]][]=sd[x][];
     Dfs(ls[x]); Dfs(rs[x]);
 }

 ll dfs(ll l,ll r){
     ll x=++nd; L[x]=l; R[x]=r;
     for (ll i=; fa[fa[x][i]][i]; i++) fa[x][i+]=fa[fa[x][i]][i];
     if (l==r) return pos[l]=x;
     ll m=mid[tot++];
     fa[nd+][]=x; ls[x]=dfs(l,m);
     fa[nd+][]=x; rs[x]=dfs(m+,r);
     return x;
 }

 ll getl(ll l){
     ll lc=lca(l,u),x=dep[lc]*(sm[l][]-sm[lc][])+(bel(l,ls[lc]) && lc!=u)+sd[lc][]-sm[lc][];
     return sd[l][]+sm[l][]*dep[u]-x*;
 }

 ll getr(ll r){
     ll lc=lca(r,u),x=dep[lc]*(sm[r][]-sm[lc][])+(bel(r,rs[lc]) && lc!=u)+sd[lc][]-sm[lc][];
     return sd[r][]+sm[r][]*dep[u]-x*;
 }

 int main(){
     freopen("segment.in","r",stdin);
     freopen("segment.out","w",stdout);
     scanf("%lld",&n);
     for (ll i=; i<=n; i<<=) S++;
     for (ll i=; i<n; i++) scanf("%lld",&mid[i]);
     tot=; dfs(,n); Dfs();
     for (scanf("%lld",&m); m--; ){
         scanf("%lld%lld%lld",&u,&l,&r); l--; r++;
         if (!l && r>n) { printf("%lld\n",dep[u]); continue; }
         ll ans=;
         if (l) ans+=getl(pos[l])-((r<=n)?getl(ls[lca(pos[l],pos[r])]):);
         if (r<=n) ans+=getr(pos[r])-(l?getr(rs[lca(pos[l],pos[r])]):);
         printf("%lld\n",ans);
     }
     return ;
 }