POJ 2104 && POJ 2761 (静态区间第k大，主席树)

查询区间第K大，而且没有修改。

使用划分树是可以做的。

作为主席树的入门题，感觉太神奇了，Orz

 /* ***********************************************
 Author        :kuangbin
 Created Time  :2013-9-4 20:13:20
 File Name     :POJ2104.cpp
 ************************************************ */

 #include <stdio.h>
 #include <string.h>
 #include <iostream>
 #include <algorithm>
 #include <vector>
 #include <queue>
 #include <set>
 #include <map>
 #include <string>
 #include <math.h>
 #include <stdlib.h>
 #include <time.h>
 using namespace std;

 const int MAXN = ;
 const int M = MAXN * ;
 int n,q,m,tot;
 int a[MAXN], t[MAXN];
 int T[M], lson[M], rson[M], c[M];

 void Init_hash()
 {
     for(int i = ; i <= n;i++)
         t[i] = a[i];
     sort(t+,t++n);
     m = unique(t+,t++n)-t-;
 }
 int build(int l,int r)
 {
     int root = tot++;
     c[root] = ;
     if(l != r)
     {
         int mid = (l+r)>>;
         lson[root] = build(l,mid);
         rson[root] = build(mid+,r);
     }
     return root;
 }
 int hash(int x)
 {
     return lower_bound(t+,t++m,x) - t;
 }
 int update(int root,int pos,int val)
 {
     int newroot = tot++, tmp = newroot;
     c[newroot] = c[root] + val;
     int l = , r = m;
     while(l < r)
     {
         int mid = (l+r)>>;
         if(pos <= mid)
         {
             lson[newroot] = tot++; rson[newroot] = rson[root];
             newroot = lson[newroot]; root = lson[root];
             r = mid;
         }
         else
         {
             rson[newroot] = tot++; lson[newroot] = lson[root];
             newroot = rson[newroot]; root = rson[root];
             l = mid+;
         }
         c[newroot] = c[root] + val;
     }
     return tmp;
 }
 int query(int left_root,int right_root,int k)
 {
     int l = , r = m;
     while( l < r)
     {
         int mid = (l+r)>>;
         if(c[lson[left_root]]-c[lson[right_root]] >= k )
         {
             r = mid;
             left_root = lson[left_root];
             right_root = lson[right_root];
         }
         else
         {
             l = mid + ;
             k -= c[lson[left_root]] - c[lson[right_root]];
             left_root = rson[left_root];
             right_root = rson[right_root];
         }
     }
     return l;
 }
 int main()
 {
     //freopen("in.txt","r",stdin);
     //freopen("out.txt","w",stdout);
     while(scanf("%d%d",&n,&q) == )
     {
         tot = ;
         for(int i = ;i <= n;i++)
             scanf("%d",&a[i]);
         Init_hash();
         T[n+] = build(,m);
         for(int i = n;i ;i--)
         {
             int pos = hash(a[i]);
             T[i] = update(T[i+],pos,);
         }
         while(q--)
         {
             int l,r,k;
             scanf("%d%d%d",&l,&r,&k);
             printf("%d\n",t[query(T[l],T[r+],k)]);
         }
     }
     return ;
 }