牛客练习赛7 E 珂朵莉的数列（树状数组+爆long long解决方法）

 https://www.nowcoder.com/acm/contest/38/E

题意：

思路：

 树状数组维护。从大佬那里学习了如何处理爆long long的方法。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
typedef long long ll;
const int maxn = 1000000+100;

int n;
int a[maxn],b[maxn];
ll c[maxn];

int lowbit(int x)
{
    return x&(-x);
}

void add(int x ,int d)
{
    while(x<maxn)
    {
        c[x] += d;
        x += lowbit(x);
    }
}

ll sum(int x)
{
    ll ret = 0;
    while(x>0)
    {
        ret += c[x];
        x -= lowbit(x);
    }
    return ret;
}

int main()
{
    //freopen("in.txt","r",stdin);
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&a[i]);
        b[i] = a[i];
    }
    sort(b+1,b+n+1);
    int num = unique(b+1,b+n+1)-(b+1);
    ll ans1 = 0, ans2 = 0;
    ll mx = 1e18;
    for(int i=1;i<=n;i++)
    {
        a[i] = lower_bound(b+1,b+n+1,a[i])-(b+1);
        a[i]++;
        ans1 += (ll)(n-i+1)*(sum(n)-sum(a[i]));
        if(ans1>=mx)  ans2 += ans1/mx, ans1%=mx;
        add(a[i],i);
    }
    if(ans2)  printf("%lld%018lld
",ans2,ans1);
    else printf("%lld
",ans1);
    return 0;
}