c_cpp 合并排序是建立在归并操作上的一种有效的排序算法。该算法是采用分治法（Divide and Conquer）的一个非常典型的应用。合并排序法是将两个（或两个以上）有序表合并成一个新的有序表，

Posted 2021-05-14

//2d7-1 递归实现二路归并排序(递归实现的合并排序)
#include "stdafx.h"
#include <iostream>
using namespace std;

int a[] = {10,5,9,4,3,7,8};
int b[7];

template <class Type>
void Merge(Type c[],Type d[],int l,int m,int r);

template <class Type>
void MergeSort(Type a[],int left,int right);

int main()
{
    for(int i=0; i<7; i++)
    {
        cout<<a[i]<<" ";
    }
    cout<<endl;
    MergeSort(a,0,6);
    for(int i=0; i<7; i++)
    {
        cout<<a[i]<<" ";
    }
    cout<<endl;
}

template <class Type>
void Merge(Type c[],Type d[],int l,int m,int r)
{
    int i = l,j = m + 1,k = l;
    while((i<=m)&&(j<=r))
    {
        if(c[i]<=c[j])
        {
            d[k++] = c[i++];
        }
        else
        {
            d[k++] = c[j++];
        }
    }

    if(i>m)
    {
        for(int q=j; q<=r; q++)
        {
            d[k++] = c[q];
        }
    }
    else
    {
        for(int q=i; q<=m; q++)
        {
            d[k++] = c[q];
        }
    }
}

template <class Type>
void MergeSort(Type a[],int left,int right)
{
    if(left<right)
    {
        int i = (left + right)/2;
        MergeSort(a,left,i);
        MergeSort(a,i+1,right);
        Merge(a,b,left,i,right);//合并到数组b

        //复制回数组a
        for(int g=left; g<=right; g++)
        {
            a[g] = b[g];
        }
    }
}

//2d7-1 自然二路归并排序(合并排序非递归实现)
#include "stdafx.h"
#include <iostream>
using namespace std;

int a[] = {10,5,9,4,3,7,8};
int b[7];

template <class Type>
void Merge(Type c[],Type d[],int l,int m,int r);

template <class Type>
void MergePass(Type x[],Type y[],int s,int n);

template <class Type>
void MergeSort(Type a[],int n);

int main()
{
    for(int i=0; i<7; i++)
    {
        cout<<a[i]<<" ";
    }
    cout<<endl;
    MergeSort(a,7);
    for(int i=0; i<7; i++)
    {
        cout<<a[i]<<" ";
    }
    cout<<endl;
}

template <class Type>
void Merge(Type c[],Type d[],int l,int m,int r)
{
    int i = l,j = m + 1,k = l;
    while((i<=m)&&(j<=r))
    {
        if(c[i]<=c[j])
        {
            d[k++] = c[i++];
        }
        else
        {
            d[k++] = c[j++];
        }
    }

    if(i>m)
    {
        for(int q=j; q<=r; q++)
        {
            d[k++] = c[q];
        }
    }
    else
    {
        for(int q=i; q<=m; q++)
        {
            d[k++] = c[q];
        }
    }
}

template <class Type>
//合并大小为s的相邻子数组
void MergePass(Type x[],Type y[],int s,int n)
{
    int i = 0;
    while(i<=n-2*s)
    {
        //合并大小为s的相邻两段子数组
        Merge(x,y,i,i+s-1,i+2*s-1);
        i = i + 2*s;
    }
    //剩下的元素个数少于2s
    if(i+s<n)
    {
        Merge(x,y,i,i+s-1,n-1);
    }
    else
    {
        for(int j=i; j<=n-1; j++)
        {
            y[j]=x[j];
        }
    }
}

template <class Type>
void MergeSort(Type a[],int n)
{
    Type *b = new Type[n];
    int s = 1;
    while(s<n)
    {
        MergePass(a,b,s,n);//合并到数组b
        s += s;
        MergePass(b,a,s,n);//合并到数组a
        s += s;
    }
}