2-路归并排序的递归实现和非递归实现

#include <iostream>
#include<algorithm>
using namespace std;
const int maxn=101;
int t[maxn];
void merge(int a[],int l1,int r1,int l2,int r2) {
  //将相邻两区间合并,l2=r1+1
  int i=l1,j=l2,k=0;
  while(i<=r1&&j<=r2){
    if(a[i]<=a[j])
      t[k++]=a[i++];
    else
    t[k++]=a[j++];    
  }
  while(i<=r1)t[k++]=a[i++];
  while(j<=r2)t[k++]=a[j++];
  for(int m=l1,f=0;m<=r2;) 
  a[m++]=t[f++];
}
void mergesort(int a[],int left,int right) {          //递归实现 
  if(left<right){
    int mid=(left+right)/2;
    mergesort(a,left,mid);
    mergesort(a,mid+1,right);
    merge(a,left,mid,mid+1,right);  
  } 
}
void mergesortnot(int a[],int n) {                   //非递归实现 
  for(int step=2;step/2<n;step*=2) {
    for(int i=0;i<n;i+=step)
    {
      int mid=i+step/2-1;
      if(mid+1<n)
      merge(a,i,mid,mid+1,min(i+step-1,n-1));   
    }
  }
}
int main(){
    int a[6]={5,7,6,8,3,1};
  mergesort(a,0,5);
  for(int i=0;i<6;i++)
  cout<<a[i]<<" ";
  cout<<endl; 
   int b[6]={5,7,6,8,3,1};
  mergesortnot(b,6);
  for(int i=0;i<6;i++)
  cout<<b[i]<<" ";
  cout<<endl; 
  return 0; 
}