CLRS2.4__逆序对

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#include<iostream>

using namespace std;

 

 

int main(int argc,char* argv[])

{

    int Merge_Count(int*,int,int);

    int merge(int*,int,int,int);

 

    int A[]={2,3,8,6,1};

 

    cout<<Merge_Count(A,0,4)<<endl;;

 

    system("pause");

    return 0;

}

 

int Merge(int* A,int p,int q,int r)

{

    int n1=q-p;

    int n2=r-q;

    int i,j;

 

    int *L=new int[n1+1]();

    int* R=new int[n2+1]();

 

    for(i=0;i<n1;i++)

        L[i]=A[p+i];

    for(i=0;i<n2;i++)

        R[i]=A[q+i+1];

 

    L[n1]=INT_MAX;

    R[n2]=INT_MAX;

 

    i=0;j=0;

    int inversion=0;

    bool counted=false;

    for(int k=p;k<=r;k++)

    {

        if(counted==false && L[i]>R[j])

        {

            inversion+=n1-i+1;

            counted=true;

        }

        if(L[i]<R[j])

            i++;

        else

        {

            j++;

            counted=false;

        }

    }

    delete []L;

    delete []R;

 

    return inversion;

}

 

int Merge_Count(int* A,int p,int r)

{

    int count=0;

    if(p<r)

    {

        int q=(p+r)/2;

        int l1=Merge_Count(A,p,q);

        int l2=Merge_Count(A,q+1,r);

        count=l1+l2+Merge(A,p,q,r);

    }

    return count;

}