POJ 1990 MooFest（树状数组）

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <string>
#include <map>
#include <stack>
#include <queue>
#include <vector>
#define inf 0x3f3f3f3f
#define met(a,b) memset(a,b,sizeof a)
#define pb push_back
typedef long long ll;
using namespace std;
const int N = 2e4+10;
const int M = 24005;
const int mod=1e9+7;
ll tree[2][N];
int n,m;
struct man{
    int x,v;
    bool operator< (const man &it)const{
        return v<it.v;
    }
}a[N];
void add(int k,int num){
    while(k<=20000){
        tree[1][k]+=num;
        tree[0][k]+=1;
        k+=k&(-k);
    }
}
ll Sum(int k,int d){
    ll sum=0;
    while(k>0){
        sum+=tree[d][k];
        k-=k&(-k);
    }
    return sum;
}
int main() {
    scanf("%d",&n);
    int v,x;
    for(int i=1;i<=n;i++){
        scanf("%d%d",&a[i].v,&a[i].x);
    }
    sort(a+1,a+1+n);
    ll ans=0;
    for(int i=1;i<=n;i++){
        ll sump=Sum(a[i].x,0);
        ll sumx=Sum(a[i].x,1);
        ans+=a[i].v*(sump*a[i].x-sumx)+a[i].v*(Sum(20000,1)-sumx-(i-1-sump)*a[i].x);
        add(a[i].x,a[i].x);
    }
    printf("%lld\n",ans);
    return 0;
}