hdu 1394 Minimum Inversion Number

#include<stdio.h>
int main()
{
    int n,i,a[5024],j,sum,mixx;
    while(~scanf("%d",&n))
    {
        for(i=1;i<=n;i++)
            scanf("%d",&a[i]);
        sum=0;
        for(i=1;i<=n;i++)
            for(j=i+1;j<=n;j++)
                if(a[i]>a[j]) sum++;
                mixx=sum;
        for(i=n;i>0;i--)
        {
            sum-=n-1-a[i];
            sum+=a[i];
            if(sum<mixx)
                mixx=sum;
        }
        printf("%d\n",mixx);
    }
    return 0;
}

#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 N=5000+5;
int p[N];

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

int sum(int x)
{
    int ret=0;
    while(x>0)
    {
        ret+=p[x];
        x-=lowbit(x);
    }
    return ret;
}

void add(int x,int d)
{
    while(x<=N)
    {
        p[x]+=d;
        x+=lowbit(x);
    }
}
int main()
{
    int n,i,a[5005],ans,mixx;
    while(~scanf("%d",&n))
    {
        memset(p,0,sizeof(p));
        ans=0;
        for(i=1;i<=n;i++)
        {
            scanf("%d",&a[i]);
            ans+=n-1-a[i]-sum(a[i]+1);
            add(a[i]+1,1);
        }

        mixx=ans;
        for(i=n;i>=1;i--)
        {

            ans-=n-1-a[i];
            ans+=a[i];
            mixx=min(mixx,ans);
        }
        printf("%d\n",mixx);
    }
    return 0;
}

线段树版本

/* ***********************************************
Author        :xryz
Email         :523689985@qq.com
Created Time  :5-1 16:27:06
File Name     :Minimum Inversion Number�߶����汾.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 N=5000+2;
int a[N],cnt,n;

struct Tree
{
    int left,right;
    int sum;
} tree[4*N+10];


int query(int id,int l,int r)
{
    if(tree[id].left==l&&tree[id].right==r)
        return tree[id].sum;
    else
    {
        int mid=(tree[id].left+tree[id].right)/2;
        if(r<=mid) return query(id*2,l,r);
        else if(l>mid) return query(id*2+1,l,r);
        else
            return query(id*2,l,mid)+query(id*2+1,mid+1,r);

    }
}

void update(int id,int pos,int val)
{
    if(tree[id].left==tree[id].right)
    {
        tree[id].sum=val;
        return ;
    }
    else
    {
        int mid=(tree[id].left+tree[id].right)/2;

        if(pos<=mid) update(id*2,pos,val);
        else update(id*2+1,pos,val);

        tree[id].sum=tree[id*2].sum+tree[id*2+1].sum;

    }
}

void build(int id,int l,int r)
{
    tree[id].left=l;
    tree[id].right=r;
    if(l==r)
    {
        tree[id].sum=0;
    }
    else
    {
        int mid=(l+r)/2;
        build(id*2,l,mid);
        build(id*2+1,mid+1,r);
        tree[id].sum=tree[id*2].sum+tree[id*2+1].sum;
    }
}



int main()
{
    int i,minx;
    while(~scanf("%d",&n))
    {
        //a[0]=0;
        //memset(a,0,sizeof(a));
        build(1,1,n);
        cnt=0;
        for(i=1; i<=n; i++)
        {
            scanf("%d",&a[i]);
            cnt+=n-1-a[i]-query(1,1,a[i]+1);
            update(1,a[i]+1,1);
            //printf("%d\n",cnt);
        }

        minx=cnt;
        for(i=n; i>0; i--)
        {
            cnt-=n-1-a[i];
            cnt+=a[i];
            minx=min(minx,cnt);
        }
        printf("%d\n",minx);
    }
    return 0;
}

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