线段树合并 || 树状数组 || 离散化 || BZOJ 4756: [Usaco2017 Jan]Promotion Counting || Luogu P3605 [USACO17JAN]Promotion Counting晋升者计数

题面：P3605 [USACO17JAN]Promotion Counting晋升者计数

题解：这是一道万能题，树状数组 || 主席树 || 线段树合并 || 莫队套分块 || 线段树 都可以写。。记得离散化

线段树合并版：

 #include<cstdio>
 #include<cstring>
 #include<iostream>
 #include<algorithm>
 using namespace std;
 const int maxn=(1e5)+;
 int N,num_edge=,edge_head[maxn],W[maxn],lsh_cnt=,num_treenode=;
 int root[maxn],ans[maxn],u;
 struct A_{int id,data;}A[maxn];
 inline bool cmp(const A_&a,const A_&b){return a.data<b.data;}
 struct Edge{int to,nx;}edge[maxn];
 inline void Add_edge(int from,int to){
     edge[++num_edge].nx=edge_head[from];
     edge[num_edge].to=to;
     edge_head[from]=num_edge;
     return;
 }
 struct Tree{int lc,rc,l,r,cnt;}t[maxn*];
 inline void Build(int x,int l,int r,int q){
     t[x].l=l;t[x].r=r;int mid=(l+r)>>;
     if(l==r&&l==q){
         t[x].cnt=;
         return;
     }
     if(q<=mid)Build(t[x].lc=++num_treenode,l,mid,q);
     else Build(t[x].rc=++num_treenode,mid+,r,q);
     t[x].cnt=t[t[x].lc].cnt+t[t[x].rc].cnt;
     return;
 }
 inline int Merge(int u,int v){
     if(!u)return v;
     if(!v)return u;
     int l=t[u].l,r=t[u].r;
     if(l==r){
         t[u].cnt+=t[v].cnt;
         return u;
     }
     t[u].lc=Merge(t[u].lc,t[v].lc);
     t[u].rc=Merge(t[u].rc,t[v].rc);
     t[u].cnt=t[t[u].lc].cnt+t[t[u].rc].cnt;
     return u;
 }
 inline void Query(int g,int x,int ql,int qr){
     int l=t[x].l,r=t[x].r,mid=(l+r)>>,lc=t[x].lc,rc=t[x].rc;
     if(x==)return;
     if(ql<=l&&r<=qr){
         ans[g]+=t[x].cnt;
         return;
     }
     if(ql<=mid)Query(g,lc,ql,qr);
     if(qr>mid) Query(g,rc,ql,qr);
     return;
 }
 inline void Dfs(int x){
     for(int i=edge_head[x];i;i=edge[i].nx){
         int y=edge[i].to;
         Dfs(y);
         root[x]=Merge(root[x],root[y]);
     }
     if(W[x]+>lsh_cnt)ans[x]=;
     else Query(x,root[x],W[x]+,lsh_cnt);
     return;
 }
 int main(){
     scanf("%d",&N);
     for(int i=;i<=N;i++){
         scanf("%d",&A[i].data);
         A[i].id=i;
     }
     sort(A+,A+N+,cmp);
     W[A[].id]=++lsh_cnt;
     for(int i=;i<=N;i++)
         if(A[i].data!=A[i-].data)W[A[i].id]=++lsh_cnt;
         else W[A[i].id]=lsh_cnt;
     for(int i=;i<=N;i++){
         scanf("%d",&u);
         Add_edge(u,i);
     }
     for(int i=;i<=N;i++)Build(root[i]=++num_treenode,,lsh_cnt+,W[i]);
     Dfs();
     for(int i=;i<=N;i++)printf("%d\n",ans[i]);
     return ;
 }

树状数组版：

 #include<cstdio>
 #include<cstring>
 #include<iostream>
 #include<algorithm>
 #define ll long long
 #define re register
 using namespace std;
 inline int rd(){
     int x=;char c=getchar();
     while(c<''||c>'')c=getchar();
     while(c>=''&&c<=''){x=x*+c-''; c=getchar();}
     return x;
 }
 const int maxn=1e5;
 int N,P[maxn+],cnt=,num_edge=,edge_head[maxn+],F,C[maxn+];
 ll ans[maxn+];
 struct Edge{
     int to,nx;
 }edge[maxn+];
 struct Node{
     int x,id;
 }A[maxn+];
 inline bool cmp(const Node&a,const Node&b){
     if(a.x<b.x)return ;
     return ;
 }
 inline int Find(int x){
     re ll ans=;
     for(;x<=cnt;x+=x&(-x))ans+=C[x];
     return ans;
 }
 inline void Update(int x){
     for(;x>;x-=x&(-x))C[x]++;
     return;
 }
 inline void Dfs(int x){
     ans[x]-=Find(P[x]);
     for(re int i=edge_head[x];i;i=edge[i].nx) Dfs(edge[i].to);
     ans[x]+=Find(P[x]);
     Update(P[x]);
     return;
 }
 int main(){
     N=rd();
     for(re int i=;i<=N;i++){
         A[i].x=rd();
         A[i].id=i;
     }
     sort(A+,A+N+,cmp);
     for(re int i=;i<=N;i++){
         if(i==||A[i].x!=A[i-].x)cnt++;
         P[A[i].id]=cnt;
     }
     for(re int i=;i<=N;i++){
         scanf("%d",&F);
         edge[++num_edge].nx=edge_head[F];
            edge[num_edge].to=i;
         edge_head[F]=num_edge;
     }
     Dfs();
     for(re int i=;i<=N;i++)printf("%lld\n",ans[i]);
     return ;
 }

---

By:AlenaNuna