排序算法---归并排序

1.归并排序

void merge(int *arr, int start, int mid, int end)
{
    int i = start;
    int j = mid + 1;
    int k = 0;
    int len = end - start + 1;
    int *temp = new int[len];
    
    while(i <= mid && j <= end)
    {
        if(arr[i] < arr[j])
        {
            temp[k] = arr[i];
            k++;
            i++;
        }
        else
        {
            temp[k] = arr[j];
            k++;
            j++;
        }
    }
    
    while(i <= mid)
    {
        temp[k] = arr[i];
        k++;
        i++;
    }
    
    while(j <= end)
    {
        temp[k] = arr[j];
        k++;
        j++;
    }
    
    for(k = 0; k < len; k++)
    {
        arr[start + k] = temp[k];
    }
}

void _mergeSort(int *arr, int start, int end)
{
    if(start == end)
    {
        return;
    }
    
    int mid = (start + end ) / 2;
    _mergeSort(arr, start, mid);
    _mergeSort(arr, mid + 1, end);
    merge(arr, start, mid, end);
}

void mergeSort(int *arr, int n)
{
    _mergeSort(arr, 0, n - 1);
}