C++代码

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;
typedef long long ll;
const int N = 1e5 + 5;
int a[N], b[N], c[N];
int n;

//暴力枚举优化:
int main()
{
    cin >> n;
    for(int i = 1; i <= n; i ++ )
        cin >> a[i];
    for(int i = 1; i <= n; i ++ )
        cin >> b[i];
    for(int i = 1; i <= n; i ++ )
        cin >> c[i];

    int cnt[N], sa[N], sc[N];
    //求 a 每个数值个数的前缀和
    for(int i = 1; i <= n; i ++ )
        cnt[a[i]] ++;
    sa[0] = cnt[0];
    for(int i = 1; i <= N; i ++ )
        sa[i] = sa[i-1] + cnt[i];

    //求 c 每个数值个数的前缀和
    memset(cnt, 0, sizeof(cnt));
    for(int i = 1; i <= n; i ++ )
        cnt[c[i]] ++;
    sc[0] = cnt[0];
    for(int i = 1; i <= N; i ++ )
        sc[i] = sc[i-1] + cnt[i];

    int t = sc[N];
    ll res = 0;
    for(int i = 1; i <= n; i ++ ){
        res += ((ll)sa[ b[i]-1 ] * ( t - sc[b[i]] ));//注意数据范围 1e5*1e5 > int的范围 
        //cout << sa[b[i]-1] << " " << t << " " << res <<endl;
    }
    cout << res << endl;
    return 0;
}
//暴力枚举(不重不漏):三重循环判断 Ai < Bj < Ck
//时间复杂度：O(n^3)