题解

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
struct node{
    int first,second;
};
bool cmp(node a,node b){
    return a.first<b.first;
}
int main(){
    int n;
    cin>>n;
    vector<node>a(n);
    for(int i=0;i<n;i++){
        cin>>a[i].first;
        a[i].second=i+1;
    }
    sort(a.begin(),a.end(),cmp);
    long long sum=0,st=a[0].first,nd=a[0].second;
    for(int i=1;i<n;i++){
        if(a[i].first==st){
            nd^=a[i].second;
        }else{
            sum+=(long long)st*nd;
            st=a[i].first;
            nd=a[i].second;
        }
    }
    sum+=(long long)st*nd;
    cout<<sum;
    return 0;
}