校内测试-排序

题目

测试得分：　　100

主要算法 ：　　模拟，排序（归并，冒泡）

题干：

　　归并排序求逆序对

　代码

#include<stdio.h>
#include<stdlib.h>
#define LL long long 
#define FORa(i,s,e) for(LL i=s;i<=e;i++)
#define FORs(i,s,e) for(LL i=s;i>=e;i--)
#define File(name) freopen(name".in","r",stdin);freopen(name".out","w",stdout);

using namespace std;
inline LL read();

const LL N=200000;
LL n,ans,a[N+1],b[N+1];
void sort(LL l,LL r)
{
    if(l==r) return;
    LL mid=(l+r)/2,i=l,j=mid+1,k=l;
    sort(l,mid),sort(mid+1,r);
    while(i<=mid&&j<=r)
    {
        if(a[i]<=a[j]) b[k++]=a[i++];
        else ans+=mid-i+1,b[k++]=a[j++];
    }
    while(i<=mid) b[k++]=a[i++];
    while(j<=r) b[k++]=a[j++];
    FORa(i,l,r) a[i]=b[i];
}
int main()
{
    File("sort");
    n=read();
    FORa(i,1,n) a[i]=read();
    sort(1,n);
    printf("%lld
",ans);
    return 0;
}
inline LL read()
{
    register char c=getchar();register LL f(1),x(0);
    while(c<'0'||c>'9') f=c=='-'?-1:1,c=getchar();
    while(c>='0'&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();
    return x*f;
}