题目传送门
1 /*
2 题意：问选出3个数成等比数列有多少种选法
3 map：c1记录是第二个数或第三个数的选法，c2表示所有数字出现的次数。别人的代码很短，思维巧妙
4 */
5 /************************************************
6 * Author :Running_Time
7 * Created Time :2015-8-6 1:07:18
8 * File Name :C.cpp
9 ************************************************/
10
11 #include <cstdio>
12 #include <algorithm>
13 #include <iostream>
14 #include <sstream>
15 #include <cstring>
16 #include <cmath>
17 #include <string>
18 #include <vector>
19 #include <queue>
20 #include <deque>
21 #include <stack>
22 #include <list>
23 #include <map>
24 #include <set>
25 #include <bitset>
26 #include <cstdlib>
27 #include <ctime>
28 using namespace std;
29
30 #define lson l, mid, rt << 1
31 #define rson mid + 1, r, rt << 1 | 1
32 typedef long long ll;
33 const int MAXN = 2e5 + 10;
34 const int INF = 0x3f3f3f3f;
35 const int MOD = 1e9 + 7;
36 map<ll, ll> c1, c2;
37
38 int main(void) { //Codeforces Round #Pi (Div. 2) C. Geometric Progression
39 ll ans = 0, x; ll n, k;
40 scanf ("%I64d%I64d", &n, &k);
41 for (int i=1; i<=n; ++i) {
42 scanf ("%I64d", &x);
43 if (x % (k * k) == 0) ans += c1[x/k]; //x可选作第三个数
44 if (x % k == 0) c1[x] += c2[x/k]; //x第三个数或第二个数
45 c2[x]++;
46 }
47
48 printf ("%I64d
", ans);
49
50 return 0;
51 }