Implementation and testing of merge sort

Merge sorting method: Merge two (or more) ordered lists into a new ordered list, that is, divide the sequence to be sorted into several subsequences, and each subsequence is ordered. Then, the ordered subsequences are merged into the overall ordered sequence. A division process is always called
during the execution process until the subsequence is empty or has only one element. A total of log2n recursion is required. In the process of merging, the merge length is 2. , 4... until the whole sequence is ordered

Merge icon

Merge realization

#define MAXSIZE 20  //默认定义数据大小为20
#define T int

typedef T Seqlist[MAXSIZE];

void merge(Seqlist &L,Seqlist &sq,int left,int mid,int right)//合并
{
    for(int i = left;i<=right;++i)   //赋值
    {
        sq[i] = L[i];
    }
    int s1 = left;
    int s2 = mid + 1;
    int k = left;
    while(s1<=mid && s2 <=right)
    {
        if(sq[s1]<=sq[s2])
        {
            L[k++] = sq[s1++];
        }
        else
        {
            L[k++]= sq[s2++];
        }
    }
    while(s1 <= mid)//左边还有值，而右边已经到达界限
    {
        L[k++] = sq[s1++];
    }
    while(s2 <= right)
    {
        L[k++] = sq[s2++];
    }
}

void Merge_sort(Seqlist &L,Seqlist &sq,int left,int right)
{
    if(left >= right)
    return;
    int mid = (left + right)/2;//将数据分为两部分
    Merge_sort(L,sq,left,mid);//对左边数据进行归并排序
    Merge_sort(L,sq,mid+1,right);//对右边数据进行归并排序
    merge(L,sq,left,mid,right);//将左右两部分数据进行合并
}

merged test files

void main()  //归并排序测试
{
    Seqlist L = {16,33,9,8,25,21,3,49,5};
    Seqlist sq;
    int n = 9;
    Merge_sort(L,sq,0,8);
    for(int i = 0;i < n;++i)  
    {
        cout<<L[i]<<"  ";
    }
}

The main problem with merge sort is that it requires an auxiliary space as large as the original data. Merge sort is a stable sorting method.