归并排序

 

#include <iostream>
#include <vector>

using namespace std;

void merge(vector<int> &arr,int L,int mid,int R)
{
    int *help = new int(R-L+1);
    int p1=L,p2=mid+1,i=0;
    while(p1<=mid && p2<=R)
    {
        help[i++] = arr[p1]>arr[p2] ? arr[p2++] : arr[p1++];
    }
    while(p1<=mid)
        help[i++] = arr[p1++];
    while(p2<=R)
        help[i++] = arr[p2++];

    for (int i=0;i<R-L+1;i++)
    {
        arr[L+i] = help[i];
    }
}
void sortprocess(vector<int> &arr,int L,int R)
{
    if (L < R)
    {
        int mid = L + ((R-L)>>2);  //  (L+R)/2
        sortprocess(arr,L,mid);
        sortprocess(arr,mid+1,R);
        merge(arr,L,mid,R);
    }
}

void MergeSort(vector<int> &arr,int L,int R)
{
    if (arr.size()<2)
        return;
    sortprocess(arr,L,R);
}


int main()
{
    vector<int> arr;
    int n,temp;
    cin>>n;  //输入n个数
    for (int i=0;i<n;i++)
    {
        cin>>temp;  //输入数据
        arr.push_back(temp);
    }

    MergeSort(arr,0,arr.size()-1);

    for(int i=0;i<arr.size();i++)
        cout<<arr[i]<<endl;

    system("pause");
    return 0;

}