归并排序算法

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非递归算法如下：

#include <iostream>
#include<fstream>
#include<ctime>
#include<cstdlib>
using namespace std;

void Merge_Sort(int n,int r[],int r1[]);
void Merge(int r[],int r1[],int s,int m,int t);
void Init(int n,int *r,int * r1);
void Init(int n,int *r,int * r1)
{
    int x;
    srand((unsigned)time(NULL));
    FILE *fp;
    fp=fopen("hello.txt","w+");
    fprintf(fp,"%d ",n);

    for(int i=1;i<=n;i++)
    {
      x=rand() %1000;
       fprintf(fp,"%d ",x);
    }
    rewind(fp);
    fscanf(fp," %d",&n);
    for(int i=0;i<n;i++)
        fscanf(fp," %d",&r[i]);
}
int main()
{
    int n;
    srand((unsigned)time(NULL));
    cout << "how many" << endl;
    cin>>n;
   int *r=(int *)malloc(n*sizeof(int));
    int *r1=(int *)malloc(n*sizeof(int));
    Init(n,r,r1);
    Merge_Sort(n,r,r1);
    for(int i=0;i<n;i++)
        cout<<r[i]<<" ";
        free(r);
        free(r1);
            return 0;
}
void Merge_Sort(int n,int r[],int r1[])
{
    int length=1;
    while(length<=n)
    {
int i;
        for(i=0;i+2*length<=n;i=i+2*length)

            Merge(r,r1,i,i+length-1,i+2*length-1);

        if((i+length)<=(n-1))
            Merge(r,r1,i,i+length-1,n-1);
        length*=2;
    }
}
void Merge(int r[],int r1[],int s,int m,int t)
{
    int i=s,j=m+1,k=s;
    while(i<=m&&j<=t)
    {
        if(r[i]<=r[j])
            r1[k++]=r[i++];
        else
        {
            r1[k++]=r[j++];
        }
    }
    while(i<=m)
        r1[k++]=r[i++];
    while(j<=t)
        r1[k++]=r[j++];
    for(int l=s;l<=t;l++)
        r[l]=r1[l];

}

运行演示：

递归算法

#include <iostream>
#include<ctime>
#include<cstdlib>
#include<fstream>
using namespace std;
void Merge(int r[],int r1[],int s,int m,int t);
void Merge_Sort(int r[],int r1[],int s,int t);
void Init(int n,int *r,int * r1);
void Init(int n,int *r,int * r1)
{
    int x;
     srand((unsigned)time(NULL));
    FILE *fp;
    fp=fopen("hello.txt","w+");
    fprintf(fp,"%d ",n);
    cout<<"Êý¾Ý˳Ðò:1.Ëæ»ú  2.ÕýÐò  3ÄæÐò£º";
    int l;
    cin>>l;
    switch(l)
    {
    case 1:
        {
           srand((unsigned)time(NULL));
    for(int i=1;i<=n;i++)
    {
      x=rand() %1000;
       fprintf(fp,"%d ",x);
    }
    rewind(fp);
    fscanf(fp," %d",&n);
    for(int i=0;i<n;i++)
        fscanf(fp," %d",&r[i]);
        }

    case 2:
        {
             for(int i=1;i<=n;i++)
    {

       fprintf(fp,"%d ",i);
    }
    rewind(fp);
    fscanf(fp," %d",&n);
    for(int i=0;i<n;i++)
        fscanf(fp," %d",&r[i]);
        }

    case 3:
        {
             for(int i=n;i>=1;i--)
    {

       fprintf(fp,"%d ",i);
    }
    rewind(fp);
    fscanf(fp," %d",&n);
    for(int i=0;i<n;i++)
        fscanf(fp," %d",&r[i]);
        }
        }
}
int main()
{
    int n;
    srand((unsigned)time(NULL));
    cout << "how many" << endl;
    cin>>n;
   int *r=(int *)malloc(n*sizeof(int));
    int *r1=(int *)malloc(n*sizeof(int));
    Init(n,r,r1);
    Merge_Sort(r,r1,0,n-1);
    for(int i=0;i<n;++i)
        cout<<r[i]<<" ";

    return 0;
}
void Merge_Sort(int r[],int r1[],int s,int t)
{
    if(s==t)
        return;
    else{
        int m=(s+t)/2;
        Merge_Sort(r,r1,s,m);
        Merge_Sort(r,r1,m+1,t);
        Merge(r,r1,s,m,t);
    }

}
void Merge(int r[],int r1[],int s,int m,int t)
{
    int i=s,j=m+1,k=s;
    while(i<=m&&j<=t)
    {
        if(r[i]>r[j])
            r1[k++]=r[j++];
        else
            r1[k++]=r[i++];
    }
    while(i<=m)
        r1[k++]=r[i++];
    while(j<=t)
        r1[k++]=r[j++];
    for(int l=s;l<=t;l++)
        r[l]=r1[l];
}

运行演示：