HDU 1394 Minimum Inversion Number

/* ***********************************************
Author        :Zhou Zhentao
Email         :774388357@qq.com
Created Time  :2015/11/20 17:21:35
File Name     :acm.cpp
************************************************ */

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <time.h>
using namespace std;

const int INF=0x7FFFFFFF;
#define lson l , m , rt << 1
#define rson m + 1 , r , rt << 1 | 1
#define root 1 , N , 1
#define LL long long
const int maxn = 50000+10;
int a[maxn];
LL add[maxn<<2];
LL sum[maxn<<2];
void PushUp(int rt) {
sum[rt] = sum[rt<<1] + sum[rt<<1|1];
}
void PushDown(int rt,int m) {
if (add[rt]) {
add[rt<<1] += add[rt];
add[rt<<1|1] += add[rt];
sum[rt<<1] += add[rt] * (m - (m >> 1));
sum[rt<<1|1] += add[rt] * (m >> 1);
add[rt] = 0;
}
}
void build(int l,int r,int rt) {
add[rt] = 0;
if (l == r) {
scanf("%lld",&sum[rt]);
return ;
}
int m = (l + r) >> 1;
build(lson);
build(rson);
PushUp(rt);
}
void update(int L,int R,int c,int l,int r,int rt) {
if (L <= l && r <= R) {
add[rt] += c;
sum[rt] += (LL)c * (r - l + 1);
return ;
}
PushDown(rt , r - l + 1);
int m = (l + r) >> 1;
if (L <= m) update(L , R , c , lson);
if (m < R) update(L , R , c , rson);
PushUp(rt);
}
LL query(int L,int R,int l,int r,int rt) {
if (L <= l && r <= R) {
return sum[rt];
}
PushDown(rt , r - l + 1);
int m = (l + r) >> 1;
LL ret = 0;
if (L <= m) ret += query(L , R , lson);
if (m < R) ret += query(L , R , rson);
return ret;
}
int main()
{
int N;
while(~scanf("%d",&N))
{
memset(add,0,sizeof add);
memset(sum,0,sizeof sum);
int k=0,ans=INF;
for(int i=1;i<=N;i++)
{
scanf("%d",&a[i]);a[i]++;
update(a[i] , a[i] , 1 , root);
if(a[i]==1) continue;
k=k+(a[i]-1-query(1 , a[i]-1 ,root));
}
if(k<ans) ans=k;
for(int i=1;i<=N-1;i++)
{
k=k-(a[i]-1)+(N-a[i]);
if(k<ans) ans=k;
}
printf("%d\n",ans);
}
return 0;
}