归并代码30求调

ultimate_regular @ 2023-04-16 19:12:45

#include <bits/stdc++.h>
using namespace std;
int a[500005],b[500005];
long long ans;
void dhysb(int l,int r){
    if(l==r)    return ;
    long long mid=l+(r-l)/2;
    dhysb(l,mid);
    dhysb(mid+1,r);
    long long p=l,q=mid+1,t=l-1;
    while(p<=mid&&q<=r){
        if(a[p]<a[q])   b[++t]=a[p++];
        else {
                ans+=mid-p+1;
                b[++t]=a[q++];
            }
    }
    while(p<=mid)   b[++t]=a[p++];
    while(q<=r)     b[++t]=a[q++];
    for(int i=l;i<=r;i++)   
        a[i]=b[i];

}
int main()
{
    int n;
    cin>>n;
    for(int i=1;i<=n;i++)
        cin>>a[i];
    dhysb(1,n);
    cout<<ans;
    return 0;
}

by Lovely_CCCyh___ @ 2023-04-16 19:14:46

#include<bits/stdc++.h>
using namespace std;
int n,a[500005],b[500005];
long long ans;
void msort(int l,int r)
{
    if(l==r)
        return;
    int mid=(l+r)/2,i=l,j=mid+1,k=l;
    msort(l,mid),msort(mid+1,r);
    while(i<=mid&&j<=r)
        if(a[i]<=a[j])
            b[k++]=a[i++];
        else
            b[k++]=a[j++],ans+=mid-i+1;
    while(i<=mid)
        b[k++]=a[i++];
    while(j<=r)
        b[k++]=a[j++];
    for(int i=l;l<=r;l++)
        a[l]=b[l];
}
int main()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
        scanf("%d",&a[i]);
    msort(1,n);
    printf("%lld",ans);
    return 0;
}

by ultimate_regular @ 2023-04-16 20:36:50

@cyh114514 感谢大佬qwq,已关注