<textarea readonly="readonly" name="code" class="c">
//归并排序求逆序数
#include<stdio.h>
#include<string.h>
int a[1000005],b[1000005];
long long count;//记录逆序数
void merge(int low,int mid,int high)
{
int i=low,j=mid+1,k=low;
while((i<=mid)&&(j<=high))
{
if(a[i]<=a[j])
{
b[k++]=a[i++];
}
else
{
b[k++]=a[j++];
count+=mid-i+1;//记录逆序数
}
}
while(i<=mid)
b[k++]=a[i++];
while(j<=high)
b[k++]=a[j++];
for(int i=low; i<=high; i++)
a[i]=b[i];
}
void sort(long long low,long long high)
{
int mid=(low+high)/2;
int x,y,z;
if(low>=high)
return ;
sort(low,mid);
sort(mid+1,high);
merge(low,mid,high);
return ;
}
int main()
{
int N;
while(scanf("%d",&N)!=EOF)
{
count=0;
for(int i=0; i<N; i++)
scanf("%d",&a[i]);
sort(0,N-1);
printf("%lld\n",count);
}
return 0;
}
</textarea>
归并排序求逆序数
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转载自blog.csdn.net/zhangwei527/article/details/79009193
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