HDU5497 Inversion

#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define se second
#define fs first
#define LL long long
#define CLR(x) memset(x,0,sizeof x)
#define MC(x,y) memcpy(x,y,sizeof(x))  
#define SZ(x) ((int)(x).size())
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1 
typedef pair<int,int> P;
const double eps=1e-9;
const int maxn=100050;
const int mod=1e9+7;
const int INF=1e9;

LL read()
{
    LL x=0,f=1;char ch=getchar();
    while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
    while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
    return x*f;
}

int n,m,a[maxn];
LL c[maxn],b[maxn];

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

void add(int x,int v,LL* c){
    while(x){
        c[x]+=v;
        x-=lowbit(x);
    }
}

LL sum(int x,LL* c){
    LL cnt=0;
    while(x<=n){
        cnt+=c[x];
        x+=lowbit(x);
    }
    return cnt;
}

int main(){
    int T;
    T=read();
    while(T--){
        n=read();m=read();
        for(int i=1;i<=n;i++) a[i]=read();
        memset(b,0,(n+3)*sizeof(LL));
        memset(c,0,(n+3)*sizeof(LL));
        LL ans=0;
        for(int i=m+1;i<=n;i++){
            ans+=sum(a[i]+1,c);
            add(a[i],1,c);
        }
        LL Min=ans;
        for(int i=1;i<=n-m;i++){
            int l=i,r=i+m;
            LL tmp=ans;
            tmp+=sum(a[l]+1,b);  
            add(a[r],-1,c);
            tmp+=n-m-i-sum(a[l],c);
            tmp-=sum(a[r]+1,b);
            tmp-=n-m-i-sum(a[r],c);
            add(a[l],1,b);
            Min=min(Min,tmp);
            ans=tmp;
        }
        printf("%lld\n",Min);
    }
    return 0;
}