bzoj3524/2223 主席树

#include<iostream>
#include<cstdio>
using namespace std;
struct zxs{
int l,r,cnt;
}tree[10000005];
int tot=0;
void insert(int l,int r,int x,int &y,int v)
{
y=++tot;
tree[y]=tree[x];
tree[y].cnt++;
if(l==r) return;
int mid=(l+r)>>1;
if(v<=mid)insert(l,mid,tree[y].l,tree[y].l,v);
else    insert(mid+1,r,tree[y].r,tree[y].r,v);
}
int Rt[500005];
int ask(int l,int r,int x,int y,int T)
{
if(l==r) return l;
int mid=(l+r)>>1;
int L1=tree[y].l,L2=tree[x].l;
if(tree[L1].cnt-tree[L2].cnt>T)
return ask(l,mid,L2,L1,T);
int R1=tree[y].r,R2=tree[x].r;
if(tree[R1].cnt-tree[R2].cnt>T)
return ask(mid+1,r,R2,R1,T);
return 0;
}
void read(int &a)
{
a=0;
char c=getchar();
while(c<'0'||c>'9')
c=getchar();
while(c>='0'&&c<='9')
{
a*=10;a+=c-'0';
c=getchar();
}
}
int main()
{
int n,m,x;
scanf("%d%d",&n,&m);
for(int i=1;i<=n;i++)
{
read(x);
insert(1,n,Rt[i-1],Rt[i],x);
}
int l,r;
for(int i=1;i<=m;i++)
{
read(l);read(r);
printf("%d\n",ask(1,n,Rt[l-1],Rt[r],(r-l+1)>>1));
}
return 0;
}