https://ac.2333.moe/Problem/view.xhtml?id=1723

有三个数组A，B，C，每个数组中有n个数，你可以从每个数组中找一个数，使得Ai<Bj<Ck ,(1<=I,j,k<=n)(1<=n<=100000,1<=Ai,Bj,Ck<=1000000)，求最多可以组出多少三元组

Input

有多组输入 
第一行输入n 
接下来三行输入A，B，C三个数组，每个数组n个数 

Output

每行一个整数，表示最多有多少三元组

Sample Input

3
1 1 1
2 2 2
3 3 3
3
1 2 3
1 2 3
1 2 3

Sample Output

27
1

---

#include<iostream>
#include<algorithm>
using namespace std;const int N = 100005;
int a[N], b[N], c[N];
int main()
{int n;while(cin >> n){long long ans = 0;for(int i = 1; i <= n; i++)scanf("%d", a+i);	sort(a+1, a+n+1);for(int i = 1; i <= n; i++)scanf("%d", b+i);	sort(b+1, b+n+1);for(int i = 1; i <= n; i++)scanf("%d", c+i);	sort(c+1, c+n+1);for(int i = 1; i <= n; i++){int k1 = lower_bound(a+1, a+n+1, b[i]) - a;int k2 = upper_bound(c+1, c+n+1, b[i]) - c;//	while(c[k2] == b[i] && k2 <= n) k2++;//	cout << k1-1 << ' ' << k2 << endl;ans +=(long long) (n-k2+1)*(k1-1);}cout << ans << endl;}return 0;
}
/*
3
1 1 1
2 2 2
3 3 3
3
1 2 3
1 2 3
1 2 3
*/