Binary Indexed Tree 分类： ACM TYPE 2014-08-29 13:08 99人阅读 评论(0) 收藏

    #include<iostream>
    #include<cstring>
    #include<cstdio>
    using namespace std;
    int n, m;
    int num[100005];
    int front(int x)
    {
        return x&(-x);
    }

    int update(int x,int k)
    {
        while(x<=n)
        {
            num[x]+=k;
            x+=front(x);
        }
        return 1;
    }

    int sum(int x)
    {
        int s = 0;
        while(x>0)
        {
            s+=num[x];
            x-=front(x);
        }
        return s;
    }

    int main()
    {
        int a, b, c;
        int cur[5005];
        while(scanf("%d",&n)!=EOF)
        {
            memset(num,0,sizeof(num));
            memset(cur,0,sizeof(cur));
            b = 0;
            for(int i=1;i<=n;i++)
            {
                scanf("%d",&cur[i]);
                cur[i]++;
                b+=(i-sum(cur[i])-1);
                update(cur[i],1);
            }
            c = b;
            for(int i=1;i<=n;i++)
            {
                b = b + (n-cur[i] +1 ) - cur[i];
                c=b<c?b:c;
            }
            printf("%d\n",c);
        }
        return 0;
    }

Code From Hdu 1394

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