题意：求最小逆序数

#include
     
      using namespace std;int c[5005],n,a[5005];int lowbit(int x){	return x&(-x);}int sum(int x){	int sum=0;	while(x>0)	{		sum+=c[x];		x-=lowbit(x);	}	return sum;}void inster(int x,int i){	while(x<=n)	{		c[x]+=i;		x+=lowbit(x);	}}int main(){	int i,s[5005],count,min;	while(scanf("%d",&n)>0)	{		memset(a,0,sizeof(a));		memset(c,0,sizeof(c));		count=0;		for(i=1;i<=n;i++)		{			scanf("%d",&a[i]);			a[i]++;			inster(a[i],1);			count+=i-sum(a[i]);		}		s[1]=count;		for(i=n;i>=2;i--)		{			count=count+2*a[i]-n-1;  //把第n个数移到第一位，所以，从i=n开始；那么，要减去在它前面比它大的逆序数的个数，还要加上当它排第一位时，在它后面比它小的数的个数			s[i]=count;		}		min=s[1];		for(i=2;i<=n;i++)			if(min>s[i])				min=s[i];		printf("%d\n",min);	}	return 0;}