C++实现归并排序

implementing merge sort in C++(C++实现归并排序)

问题描述

我研究了归并排序的理论，但不知道如何在 C++ 中实现它.我的问题是，合并排序以递归方式创建数组.但是在实现的时候，我们如何在运行时创建数组呢?或者对此的一般方法是什么?

I have studied the theory of the merge sort but don't have any idea of how to implement it in C++. My question is, merge sort creates arrays in recursion. But when implementing, how do we create arrays in runtime? or what is the general approach for this?

谢谢.

推荐答案

基于这里的代码:http://cplusplus.happycodings.com/algorithms/code17.html

// Merge Sort

#include <iostream>
using namespace std;

int a[50];
void merge(int,int,int);
void merge_sort(int low,int high)
{
 int mid;
 if(low<high)
 {
  mid = low + (high-low)/2; //This avoids overflow when low, high are too large
  merge_sort(low,mid);
  merge_sort(mid+1,high);
  merge(low,mid,high);
 }
}
void merge(int low,int mid,int high)
{
 int h,i,j,b[50],k;
 h=low;
 i=low;
 j=mid+1;

 while((h<=mid)&&(j<=high))
 {
  if(a[h]<=a[j])
  {
   b[i]=a[h];
   h++;
  }
  else
  {
   b[i]=a[j];
   j++;
  }
  i++;
 }
 if(h>mid)
 {
  for(k=j;k<=high;k++)
  {
   b[i]=a[k];
   i++;
  }
 }
 else
 {
  for(k=h;k<=mid;k++)
  {
   b[i]=a[k];
   i++;
  }
 }
 for(k=low;k<=high;k++) a[k]=b[k];
}
int main()
{
 int num,i;

cout<<"*******************************************************************
*************"<<endl;
 cout<<"                             MERGE SORT PROGRAM
"<<endl;

cout<<"*******************************************************************
*************"<<endl;
 cout<<endl<<endl;
 cout<<"Please Enter THE NUMBER OF ELEMENTS you want to sort [THEN 
PRESS
ENTER]:"<<endl;
 cin>>num;
 cout<<endl;
 cout<<"Now, Please Enter the ( "<< num <<" ) numbers (ELEMENTS) [THEN
PRESS ENTER]:"<<endl;
 for(i=1;i<=num;i++)
 {
  cin>>a[i] ;
 }
 merge_sort(1,num);
 cout<<endl;
 cout<<"So, the sorted list (using MERGE SORT) will be :"<<endl;
 cout<<endl<<endl;

 for(i=1;i<=num;i++)
 cout<<a[i]<<"  ";

 cout<<endl<<endl<<endl<<endl;
return 1;

}

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