POJ-2104 K-th Number(主席树)

 1 #include <cstdio>
 2 #include <cmath>
 3 #include <cstdlib>
 4 #include <queue>
 5 #include <iostream>
 6 #include "algorithm"
 7 using namespace std;
 8 typedef long long LL;
 9 const int MAX=1e5+5;
10 int n,m;
11 int a[MAX],b[MAX],lb,root[MAX],cnt;
12 struct Node{
13     int l,r;
14     int sum;
15     Node (){l=r=sum=0;}
16 }t[MAX*40];
17 inline int read(){
18     int an=0,x=1;char c=getchar();
19     while (c<‘0‘ || c>‘9‘) {if (c==‘-‘) x=-1;c=getchar();}
20     while (c>=‘0‘ && c<=‘9‘) {an=an*10+c-‘0‘;c=getchar();}
21     return an*x;
22 }
23 void update(int l,int r,int &x,int y,int pos){
24     t[++cnt]=t[y],t[cnt].sum++;x=cnt;
25     if (l==r) return;
26     int mid=(l+r)>>1;
27     if (pos<=mid) update(l,mid,t[x].l,t[y].l,pos);
28     else update(mid+1,r,t[x].r,t[y].r,pos);
29 }
30 int query(int l,int r,int x,int y,int k){
31     if (l==r) return l;
32     int sum=t[t[y].l].sum-t[t[x].l].sum;
33     int mid=(l+r)>>1;
34     if (sum>=k) return query(l,mid,t[x].l,t[y].l,k);
35     else return query(mid+1,r,t[x].r,t[y].r,k-sum);
36 }
37 int main(){
38     freopen ("chairman.in","r",stdin);
39     freopen ("chairman.out","w",stdout);
40     int i,j;
41     int x,y,z;
42     n=read();m=read();
43     for (i=1;i<=n;i++){a[i]=read();b[i]=a[i];}sort(b+1,b+n+1);
44     lb=unique(b+1,b+n+1)-(b+1);
45     for (i=1;i<=n;i++){
46         int pos=lower_bound(b+1,b+lb+1,a[i])-b;
47         update(1,lb,root[i],root[i-1],pos);
48     }
49     for (i=1;i<=m;i++){
50         x=read();y=read();z=read();
51         printf("%d\n",b[query(1,lb,root[x-1],root[y],z)]);
52     }
53     return 0;
54 }