POJ 2104 K-th Number

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <algorithm>
 5 using namespace std;
 6 const int maxn = 100010;
 7 struct Node {
 8     int L,R,sum;
 9 } tree[maxn<<5];
10 struct A{
11     int x,id;
12     bool operator<(const A& rhs) const{
13         return x < rhs.x;
14     }
15 }a[maxn];
16 int root[maxn],rk[maxn],tot,n,m;
17 void update(int val,int &v,int L,int R) {
18     tree[tot] = tree[v];
19     v = tot++;
20     ++tree[v].sum;
21     if(L == R) return;
22     int mid = (L + R)>>1;
23     if(val <= mid) update(val,tree[v].L,L,mid);
24     else update(val,tree[v].R,mid+1,R);
25 }
26 int query(int i,int j,int k,int L,int R) {
27     if(L == R) return L;
28     int tmp = tree[tree[j].L].sum - tree[tree[i].L].sum;
29     int mid = (L + R)>>1;
30     if(k <= tmp) return query(tree[i].L,tree[j].L,k,L,mid);
31     else return query(tree[i].R,tree[j].R,k - tmp,mid+1,R);
32 }
33 int main() {
34     while(~scanf("%d%d",&n,&m)){
35         for(int i = 1; i <= n; ++i){
36             scanf("%d",&a[i].x);
37             a[i].id = i;
38         }
39         sort(a+1,a+1+n);
40         for(int i = 1; i <= n; ++i)
41             rk[a[i].id] = i;
42         tot = 1;
43         memset(tree,0,sizeof tree);
44         root[0] = 0;
45         for(int i = 1; i <= n; ++i){
46             root[i] = root[i-1];
47             update(rk[i],root[i],1,n);
48         }
49         while(m--){
50             int i,j,k;
51             scanf("%d%d%d",&i,&j,&k);
52             printf("%d\n",a[query(root[i-1],root[j],k,1,n)].x);
53         }
54     }
55     return 0;
56 }