求助，归并排序！！！全WA

#include <iostream>
#include <algorithm>
using namespace std;

long long a[600005],tmp[600005],cnt;

void merge(long long left,long long mid,long long right)
{
    long long i=left,j=mid+1,k=left;

    while(i<=mid && j<=right)
    {
        if(a[i]<=a[j])
        {
            tmp[k++]=a[i++];
        }
        else
        {
            cnt++;
            tmp[k++]=a[j++];
        }
    }

    while(i<=mid)   
    {
        tmp[k++]=a[i++];
    }
    while(j<=right)
    {
        tmp[k++]=a[j++];
    }

    for(long long i=left;i<=right;i++)
    {
        a[i]=tmp[i];
    }
}

void mergesort(long long left,long long right)
{   
    if(left>=right)
        return ;
    long long mid=(left+right)/2;

    mergesort(left,mid);
    mergesort(mid+1,right);

    merge(left,mid,right);
}

int main()
{
    ios::sync_with_stdio(false); \\快读
    long long n;

    cin>>n;

    for(long long i=1;i<=n;i++)
        cin>>a[i];

    mergesort(1,n);

    cout<<cnt;

    return 0;
}

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