【bzoj3524】【Poi2014】【Couriers】可持久化线段树（主席树）水题

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;

const int N=500000+5;

struct Node{
Node *ls,*rs;
int sum;
}*root
,*null,pool[N*40],*tail=pool;
int n,m,aa;

Node *newnode(){
Node *rt=++tail;
rt->ls=rt->rs=null;
rt->sum=0;
return rt;
}
void insert(Node *&ndn,Node *ndp,int le,int ri,int pos){
ndn=newnode();
ndn->sum=ndp->sum+1;
if(le==ri) return ;
ndn->ls=ndp->ls,ndn->rs=ndp->rs;
int mid=(le+ri)>>1;
if(pos<=mid) insert(ndn->ls,ndp->ls,le,mid,pos);
else insert(ndn->rs,ndp->rs,mid+1,ri,pos);
}
int query(Node *ndn,Node *ndp,int le,int ri,int limit){
if(le==ri) return le;
int mid=(le+ri)>>1;
int lsum=ndn->ls->sum - ndp->ls->sum;
int rsum=ndn->rs->sum - ndp->rs->sum;
int rt=0;
if(lsum>limit) rt=query(ndn->ls,ndp->ls,le,mid,limit);
if(rsum>limit) rt=query(ndn->rs,ndp->rs,mid+1,ri,limit);
return rt;
}
int main(){
null=++tail;
null->ls=null->rs=null;
null->sum=0;
root[0]=null;

scanf("%d%d",&n,&m);
for(int i=1;i<=n;i++){
scanf("%d",&aa);
insert(root[i],root[i-1],1,n,aa);
}
int x,y;
while(m--){
scanf("%d%d",&x,&y);
printf("%d\n",query(root[y],root[x-1],1,n,(y-x+1)/2));
}
return 0;
}