hdu 1394 Minimum Inversion Number 树状数组+递推

#include
#include
#include
using namespace std;
int c[5005];
int a[5005];
int ans,n;
int lowbit(int x)
{
     return x&(-x);
}
int Sum(int end)
{
    int sum=0;
    while(end>0)
    {
         sum+=c[end];
         end=end-lowbit(end);
    }
    return sum;
}
void change(int i,int x)
{
     while(i<=n)
     {
          c[i]=c[i]+x;
          i=i+lowbit(i);
     }
}
int main()
{
    while(scanf("%d",&n)!=EOF)
    {
        int tmp=0;
        int s;
        for(int i=1;i<=n;i++)
        {
            c[i]=0;
            scanf("%d",&s);
            a[i]=s+1;
        }
        for(int i=1;i<=n;i++)
        {
            change(a[i],1);
            tmp+=(i-Sum(a[i]));
        }
        ans=tmp;
        int now;
        for(int i=1;i