D. Pashmak and Parmida’s problem 树状数组 - 服务器托管|北京服务器租用|机房托管租用|IDC托管租用|机房机柜带宽租用-价格及费用咨询

Parmida is a clever girl and she wants to participate in Olympiads this year. Of course she wants her partner to be clever too (although he’s not)! Parmida has prepared the following test problem for Pashmak.

There is a sequence a that consists of n integers a1, a2, …, an. Let’s denote f(l, r, x) the number of indices k such that: l ≤ k ≤ r and ak = x. His task is to calculate the number of pairs of indicies i, j (1 ≤ i f(j, n, aj).

Help Pashmak with the test.

Input
The first line of the input contains an integer n (1 ≤ n ≤ 106). The second line contains n space-separated integers a1, a2, …, an (1 ≤ ai ≤ 109).

Output
Print a single integer — the answer to the problem.

Examples
inputCopy
7
1 2 1 1 2 2 1
outputCopy
8
inputCopy
3
1 1 1
outputCopy
1
inputCopy
5
1 2 3 4 5
outputCopy
0

先预处理一下，然后逆序对搞一搞就好

#include
#include
#include
#include
#include
#include
#include
#include
#include
using namespace std;
#define maxn 1000005
#define inf 0x3f3f3f3f
typedef long long ll;
typedef unsigned long long int ull;

typedef pair pii;
int n;
int a[maxn];
mapmp;
int b[maxn],c[maxn];
void add(int x)
{
    for(;x>n;
    int i,j;
    for(i=1;i>a[i];
    for(i=1;i=1;i--){
        mp[a[i]]++;
        c[i]=mp[a[i]];
    }
    memset(a,0,sizeof(a));
    ll res=0;
    for(i=n-1;i>=2;i--){
        add(c[i+1]);
        res+=query(b[i]-1);
    }
    cout

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