C++ 归并 0分

Gold14526 @ 2021-10-28 21:23:35

#include<bits/stdc++.h>
using namespace std;
int n,ans;
int a[500001],c[500001];
void merge_sort(int l,int r)
{
    if(l>=r)return;
    int m=(l+r)/2;
    merge_sort(l,m);
    merge_sort(m+1,r);
    int h=l,h2=m+1;
    for(int i=l;i<=r;i++)
    {
        if(h>m)
        {
            c[h+h2-m]=a[h2++];
        }
        else if(h2>r)
        {
            c[h+h2-m]=a[h++];
        }
        else if(a[h]>a[h2])
        {
            ans+=r-h2+1;
            c[h+h2-m]=a[h++];
        }
        else
        {
            c[h+h2-m]=a[h2++];
        }
    }
}
int read()
{
    int s=0,t=1;
    char c=getchar();
    while(c<'0'||c>'9')
    {
        if(c=='-')t=-1;
        c=getchar();
    }
    while(c>='0'&&c<='9')
    {
        s=s*10+c-'0';
        c=getchar();
    }
    return s*t;
}
void out(int s)
{
    if(s==0)return;
    if(s<0)
    {
        putchar('-');
        out(-s);
        return;
    }
    out(s/10);
    putchar(s%10+'0');
}
int main()
{
    //freopen(".in","r",stdin);
    //freopen(".out","w",stdout);
    n=read();
    for(int i=1;i<=n;i++)
    {
        a[i]=read();
    }
    merge_sort(1,n);
    out(ans);
    return 0;
}

by Gold14526 @ 2021-10-28 21:26:35

第二重制版：

#include<bits/stdc++.h>
using namespace std;
int n;
long long ans;
int a[500001],c[500001];
void merge_sort(int l,int r)
{
    if(l>=r)return;
    int m=(l+r)/2;
    merge_sort(l,m);
    merge_sort(m+1,r);
    int h=l,h2=m+1;
    for(int i=l;i<=r;i++)
    {
        if(h>m)
        {
            c[h+h2-m]=a[h2++];
        }
        else if(h2>r)
        {
            c[h+h2-m]=a[h++];
        }
        else if(a[h]>a[h2])
        {
            ans+=r-h2+1;
            c[h+h2-m]=a[h++];
        }
        else
        {
            c[h+h2-m]=a[h2++];
        }
    }
}
int read()
{
    int s=0,t=1;
    char c=getchar();
    while(c<'0'||c>'9')
    {
        if(c=='-')t=-1;
        c=getchar();
    }
    while(c>='0'&&c<='9')
    {
        s=s*10+c-'0';
        c=getchar();
    }
    return s*t;
}
void out(long long s)
{
    if(s==0)return;
    if(s<0)
    {
        putchar('-');
        out(-s);
        return;
    }
    out(s/10);
    putchar(s%10+'0');
}
int main()
{
    //freopen(".in","r",stdin);
    //freopen(".out","w",stdout);
    n=read();
    for(int i=1;i<=n;i++)
    {
        a[i]=read();
    }
    merge_sort(1,n);
    out(ans);
    return 0;
}