P3834 【模板】可持久化线段树 1（主席树）

 #include <bits/stdc++.h>
 #define read read()
 #define up(i,l,r) for(int i = (l);i <= (r);i++)
 using namespace std;
 int read
 {
     int x = ,f = ; char ch = getchar();
     while(ch <  || ch > ) {if(ch == '-') f = -; ch = getchar();}
     while(ch >= && ch <=) {x =  * x + ch - ; ch = getchar();}
     return x * f;
 }
 const int N = 2e5+;
 struct a
 {
     int l,r,sum;
 }node[N*];
 int n,m,cnt,a[N],root[N];
 vector<int> v;
 int Get_id(int x) {return lower_bound(v.begin(),v.end(),x) - v.begin() + ;}
 void update(int l,int r,int &cur,int pre,int pos)
 {
     node[++cnt] = node[pre],node[cnt].sum++,cur = cnt;
     if(l==r) return;
     int mid = (l+r)>>;
     if(pos<=mid) update(l,mid,node[cur].l,node[pre].l,pos);
     else update(mid+,r,node[cur].r,node[pre].r,pos);
 }
 int query(int l,int r,int x,int y,int k)
 {
     if(l==r) return l;
     int mid = (l+r)>>;
     int lsum = node[node[y].l].sum - node[node[x].l].sum;
     if(lsum>=k) return query(l,mid,node[x].l,node[y].l,k);
     else return query(mid+,r,node[x].r,node[y].r,k-lsum);
 }
 int main()
 {
     freopen("input.txt","r",stdin);
     n = read; m = read;
     int l,r,k;
     up(i,,n) a[i] = read,v.push_back(a[i]);
     sort(v.begin(),v.end());
     v.erase(unique(v.begin(),v.end()),v.end());
     up(i,,n) update(,n,root[i],root[i-],Get_id(a[i]));
     up(i,,m)
     {
         l = read; r = read; k = read;
         printf("%d\n",v[query(,n,root[l-],root[r],k)-]);
     }
     return ;
 }