Merge_Sort C++

难点在于理解计算机执行顺序：

1. 每次拆分(MergeSort)时，beg 和 end 的值
2. 每次归并(Merge)时 L，R的内容
3. 拆分的位置 在Merge_Sort退出时，带入Merge中

执行顺序图

Merge_Sort.h

#include<vector>
#include<limits>
void Merge(std::vector<int>& A, int beg, int mid, int end) {
   
    std::vector<int> L(A.cbegin() + beg, A.cbegin() + mid + 1);
    std::vector<int> R(A.cbegin() + mid + 1, A.cbegin() + end + 1);
    int i = 0, j = 0;
    L.insert(L.end(), std::numeric_limits<int>::max());
    R.insert(R.end(), std::numeric_limits<int>::max());

    for (int k = beg; k <= end; k++) 
    {
        if (L[i] < R[j]) 
            A[k] = L[i++];
        else 
            A[k] = R[j++];
    }
}
void MergeSort(std::vector<int>& A, int beg, int end) 
{
    if (beg < end)
    {
        int mid = beg + (end - beg) / 2;
        MergeSort(A, beg, mid);
        MergeSort(A, mid + 1, end);
        Merge(A, beg, mid, end);
    }
}

main.cpp

#include"Merge_Sort.h"
#include<iostream>
using namespace std;

int main()
{
    vector<int> arr = {38,27,43,3,9,82,10};
    cout << "
 array is 
";
    for (auto i : arr)
        cout << i << " ";
    cout << endl;
        MergeSort(arr, 0, arr.size()-1);
    cout << "
Sorted array is 
";
    for (auto i : arr)
        cout << i<<" ";
    return 0;
}