P3834 【模板】可持久化线段树 1（主席树）

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 const int maxn = 2e5+5;
 4 int n, q, m, cnt = 0;
 5 int a[maxn], b[maxn], T[maxn];
 6 int sum[maxn<<5], L[maxn<<5], R[maxn<<5];
 7 inline int build(int l, int r) {
 8     int rt = ++cnt;
 9     sum[rt] = 0;
10     if (l < r) {
11         int mid = (l+r)/2;
12         L[rt] = build(l, mid);
13         R[rt] = build(mid+1, r);
14     }
15     return rt;
16 }
17 inline int update(int pre, int l, int r, int x) {
18     int rt = ++cnt;
19     L[rt] = L[pre]; R[rt] = R[pre]; sum[rt] = sum[pre]+1;
20     if (l < r) {
21         int mid = (l+r)/2;
22         if (x <= mid) L[rt] = update(L[pre], l, mid, x);
23         else R[rt] = update(R[pre], mid+1, r, x);
24     }
25     return rt;
26 }
27 inline int query(int u, int v, int l, int r, int k) {
28     if (l >= r) return l;
29     int x = sum[L[v]] - sum[L[u]];
30     int mid = (l+r)/2;
31     if (x >= k) return query(L[u], L[v], l, mid, k);
32     else return query(R[u], R[v], mid+1, r, k-x);
33 }
34 int main() {
35     scanf("%d%d",&n,&q);
36     for (int i = 1; i <= n; ++i) {
37         scanf("%d",&a[i]);
38         b[i] = a[i];
39     }
40     sort(b+1,b+1+n);
41     m = unique(b+1,b+1+n)-b-1;
42     T[0] = build(1,m);
43     for (int i = 1; i <= n; ++i) {
44         int t = lower_bound(b+1,b+1+m,a[i])-b;
45         T[i] = update(T[i-1], 1, m, t);
46     }
47     while (q--) {
48         int l, r, k;
49         scanf("%d%d%d",&l,&r,&k);
50         int t = query(T[l-1], T[r], 1, m, k);
51         printf("%d\n",b[t]);
52     }
53     return 0;
54 }