bzoj 3176: [Coci 2012]Sort

#include<cstdio>

#include<cstdlib>

#include<cstring>

#include<algorithm>

#define ll long long

#define inf 1e9

#define eps 1e-8

#define md

#define N 100010

using namespace std;

int c[N],a[N];

int n;

void add(int x)

{

for (;x<=n;x+=x&(-x)) c[x]++;

}

int qsum(int x)

{

int ans=0;

for (;x;x-=x&(-x)) ans+=c[x];

return ans;

}

int main()

{

scanf("%d",&n);

for (int i=1;i<=n;i++) scanf("%d",&a[i]);

int now=1; a[n+1]=inf;

ll ans=0;

for (int i=1;i<=n;i++)

if (a[i+1]>a[i])

{

if (i>now)

{

reverse(a+now,a+i+1);

ans++;

}

now=i+1;

}

for (int i=n;i;i--)

{

ans+=qsum(a[i]);

add(a[i]);

}

printf("%lld\n",ans);

return 0;

}