poj 1990（树状数组，另外，注意数据类型，必须是long long不能是int）

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
using namespace std;
#define ll long long
const ll maxn = 20005; 
typedef pair<ll,ll> PII;
ll nn;
PII a[maxn];
ll num[maxn],sum[maxn];
int lowbit(ll i){
    return i&(-i);
}
void upDate(ll*x,ll i,ll val){
    while(i<=nn){
        x[i] += val;
        i += lowbit(i);
    }
} 
ll getSum(ll*x,ll i){
    ll s = 0;
    while(i>0){
        s += x[i];
        i -= lowbit(i);
    }
    return s;
}
int main(){
    ll n,i,j,total,ans;
    ll nm,sm,small,big,val;
    while(scanf("%lld",&n)!=EOF){
        memset(sum,0,sizeof sum);
        memset(num,0,sizeof num);
        nn = -1;
        for(i=0;i<n;i++){
            scanf("%lld%lld",&a[i].first,&a[i].second);
            nn = max(nn,a[i].second);
        }
        sort(a,a+n);
        total = 0;
        ans = 0;
        for(i=0;i<n;i++){
            nm = getSum(num,a[i].second);
            sm = getSum(sum,a[i].second);
            small = nm*a[i].second-sm;
            big = total-sm-(i-nm)*a[i].second;
            ans += (small+big)*a[i].first;
            total += a[i].second;
            upDate(num,a[i].second,1);
            upDate(sum,a[i].second,a[i].second);
        }
        printf("%lld\n",ans);
    }
    return 0;
}