分治思想的归并排序算法

今天看了算法导论上归并排序算法部分，应用了分治思想。将书上的伪代码用C++写了出来。但书中的数组下标都是从1开始而不是我们平时使用的从0开始，所以与书中稍有不同。

代码如下（注释用英语写的，如果写汉语，会有难看下划线，实在不喜欢）：

 

#include <iostream>
using namespace std;

void merge(int M[], int l, int p, int r)
{
    int i, j, k;
    int n1 = p - l + 1;
    int n2 = r - p;
    int L[n1 + 1], R[n2 + 1];

    i = j = 0;
    while(i < n1)     //the array passed in is divided into two parts, the left part is put into array L[];
    {
 //       L[i] = M[l + i -1];   //when first loop,l=p=0,r=1.so l+i-1 is -1, error
        L[i] = M[l + i];    //the array index in the book is from 1 instead of 0,so "-1" is not needed
        ++ i;
    }
    while(j < n2)     //the right part is put into array R[]
    {
        R[j] = M[p + j + 1];     //different from it in the book, +1 is needed
        ++ j;
    }
    L[n1] = 10000;
    R[n2] = 10000;

    i = j = 0;
    for(k = l; k <= r; ++k)      //merge the array passed in
    {
        if (L[i] <= R[j])
        {
            M[k] = L[i];
            ++ i;
        }
        else
        {
            M[k] = R[j];
            ++ j;
        }
    }
}
void merge_sort(int M[], int l, int r)
{
    for(int i = 0; i < 8; ++i)
    cout << M[i] << " ";
    cout << endl;
    if(l < r)
    {
        int p = (l + r) / 2;
            cout << "p is:" << p << endl;   // these output will help understand how the array is be decomposed
        merge_sort(M, l, p);
            cout << "left p:" << p << endl;
        merge_sort(M, p + 1, r);
            cout << "right p:" << p << endl;
        // these two steps is to decompose the array so that we can use function merge(M,l,p,r) to merge it
        //when using stack, the scene will be saved, every p will be saved,when it is decomposed to the bottom, each scene will be reappear
        merge(M, l, p, r);
    }
}

int main()
{
    int A[8] = {7,6,1,34,2,5,7,3};

    merge_sort(A, 0, 7);
    for(int i = 0; i < 8; ++i)      //output the sorted array
        cout << A[i] << " ";
    cout << endl;
    return 0;
}