如題，這是一個模板。。。

 1 #include <algorithm>
 2 #include <iostream>
 3 #include <cstring>
 4 #include <cstdio>
 5 #include <cctype>
 6 #include <cmath> 
 7 
 8 inline void read(int & x)
 9 {
10     x = 0;
11     int k = 1;
12     char c = getchar();
13     while
 
 (!isdigit(c))
14         if (c == '-') c = getchar(), k = -1;
15         else c = getchar();
16     while (isdigit(c))
17         x = (x << 1) + (x << 3) + (c ^ 48),
18         c = getchar();
19     x *= k;
20 }
21 
22 const int MAXN = 202020;
23 
24 struct sgt
25 {
26     int l, r, w;
 
27 }t[MAXN << 5];
28 
29 int n, m, id = 0, cnt = 0, L, R, K;
30 int root[MAXN], a[MAXN], b[MAXN];
31 
32 inline int Lsh(int x) { return std::lower_bound(a + 1, a + cnt + 1, x) - a; }
33 
34 void Pushup(int u)
35 {
36     t[u].w = t[t[u].l].w + t[t[u].r].w;
37 }
38 
39 void Build(int u, int
 
 l, int r)
40 {
41     if (l == r)
42     {
43         t[u].l = -1;
44         t[u].r = -1;
45         t[u].w = 0;
46         return;
47     }
48     t[u].l = ++id;
49     t[u].r = ++id;
50     int mid = (l + r) >> 1;
51     Build(t[u].l, l, mid);
52     Build(t[u].r, mid + 1, r);
53     Pushup(u);
54 }
55 
56 int Add(int u, int l, int r, int k)
57 {
58     int cur = ++id;
59     t[cur].l = t[u].l;
60     t[cur].r = t[u].r;
61     t[cur].w = t[u].w + 1;
62     if (l < r)
63     {
64         int mid = (l + r) >> 1;
65         if (k <= mid) t[cur].l = Add(t[u].l, l, mid, k);
66         else t[cur].r = Add(t[u].r, mid + 1, r, k);
67     }
68     return cur;
69 }
70 
71 int Query(int u, int v, int l, int r, int k)
72 {
73     if (l == r) return l;
74     int df = t[t[v].l].w - t[t[u].l].w;
75     int mid = (l + r) >> 1;
76     if (df < k) return Query(t[u].r, t[v].r, mid + 1, r, k - df);
77     else return Query(t[u].l, t[v].l, l, mid, k);
78 }
79 
80 signed main()
81 {
82     read(n), read(m);
83     for (int i = 1; i <= n; ++i) read(a[i]), b[i] = a[i];
84     std::sort(a + 1, a + n + 1);
85     cnt = std::unique(a + 1, a + n + 1) - a - 1;
86     Build(root[0] = ++id, 1, cnt);
87     for (int i = 1; i <= n; ++i)
88         root[i] = Add(root[i - 1], 1, cnt, Lsh(b[i]));
89     for (int i = 1; i <= m; ++i)
90     {
91         read(L), read(R), read(K);
92         int p = Query(root[L - 1], root[R], 1, cnt, K);
93         printf("%d\n", a[p]);
94     }
95     return 0;
96 }