hdoj 5972 树状数组

最新推荐文章于 2020-10-23 12:27:05 发布

acblacktea

最新推荐文章于 2020-10-23 12:27:05 发布

阅读量863

点赞数

分类专栏：树状数组

本文链接：https://blog.youkuaiyun.com/acblacktea/article/details/52107963

版权

树状数组专栏收录该内容

4 篇文章

订阅专栏

#include<cstdio>
#include<algorithm>
#include<iostream>
#include<cstring>
#include<map>
#define maxn 50010
#define LL long long
using namespace std;
int sum1[maxn],sum2[maxn],a[maxn],b[maxn],n;
int getSum1(int x)
{
    int ans = 0;
    for(;x;x-=(x&(-x)))ans+=sum1[x];
    return ans;
}
void update1(int x,int flag)
{
     for(;x<=maxn;x+=(x&(-x)))sum1[x]+=flag;
}
int getSum2(int x)
{
    int ans = 0;
    for(;x;x-=(x&(-x)))ans+=sum2[x];
    return ans;
}
void update2(int x,int flag)
{
     for(;x<=maxn;x+=(x&(-x)))sum2[x]+=1;
}
LL ans,sum11,sum22;
int main()
{
    while(scanf("%d",&n)!=EOF)
    {
       memset(sum1,0,sizeof(sum1));
       memset(sum2,0,sizeof(sum2));
       map<int,int>mp;
       ans = sum11 = sum22 = 0;
       for(int i=1;i<=n;i++)
       {
           scanf("%d",&a[i]);
           b[i] = a[i];
       }
       sort(b+1,b+1+n);
       int l = unique(b+1,b+1+n)-(b+1);
       for(int i=1;i<=l;i++)mp[b[i]] = i;
       for(int i=1;i<=n;i++)a[i] = mp[a[i]];
       for(int i=1;i<=n;i++)update1(a[i],1);
       for(int i=1;i<=n;i++)
       {
           update1(a[i],-1);
           int pre1 = getSum1(a[i]-1);//a<b
           int pre2 = getSum1(n+1)-getSum1(a[i]);//c>d
           sum11+=pre1;
           sum22+=pre2;
           int pre3 = getSum2(a[i]-1);//
           int pre4 = getSum2(n+1)-getSum2(a[i]);
           ans-=pre1*pre3;
           ans-=pre2*pre4;
           ans-=pre1*pre2;
           ans-=pre3*pre4;
           update2(a[i],1);
       }
       ans+=sum11*sum22;
       printf("%I64d\n",ans);
    }
    return 0;
}