hdu 1394 线段树

http://acm.hdu.edu.cn/showproblem.php?pid=1394

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>
#include<iostream>
#include<algorithm>
using namespace std;

const int sizen=100000;
int a[sizen];
struct ele
{
    int left;
    int right;
    int sum;
}p[sizen*4];

void build(int L,int R,int step)
{
    p[step].sum=0;
    p[step].left=L;
    p[step].right=R;
    if(L!=R)
    {
        int Mid=(L+R)>>1;
        build(L,Mid,2*step);
        build(Mid+1,R,2*step+1);
    }
}

void update(int x,int step)
{
    if(p[step].left==p[step].right)
        p[step].sum=1;
    else
    {
        int Mid=(p[step].left+p[step].right)>>1;
        if(x<=Mid)
            update(x,2*step);
        else
            update(x,2*step+1);
        p[step].sum=p[2*step].sum+p[2*step+1].sum;
    }
}

int get(int x,int y,int step)
{
    if(p[step].left==x&&p[step].right==y)
        return p[step].sum;
    else
    {
        int Mid=(p[step].left+p[step].right)>>1;
        if(y<=Mid)
            return get(x,y,2*step);
        else
        if(x>=Mid+1)
            return get(x,y,2*step+1);
        else
            return get(x,Mid,2*step)+get(Mid+1,y,2*step+1);
    }
}
int main()
{
    int n;
    int i;
    int sum,Min;
    while(scanf("%d",&n)!=EOF)
    {
        sum=0;
        build(1,n,1);
        for(i=1;i<=n;i++)
        {
            scanf("%d",&a[i]);
            if(a[i]+2<=n)
                sum+=get(a[i]+2,n,1);
            update(a[i]+1,1);
        }
        Min=sum;
        for(i=1;i<n;i++)
        {
            sum-=a[i];
            sum+=(n-1-a[i]);
            if(sum<Min)
                Min=sum;
        }
        printf("%d\n",Min);
    }
    return 0;
}