算法系列——归并排序

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <math.h>
using namespace std;

void print(int a[],int n){
    for(int i=0;i<n;i++)
        cout<<a[i]<<" ";
    cout<<endl;
}

//将有二个有序数列a[first...mid]和a[mid+1...last]合并。  
void mergearray(int a[], int first, int mid, int last, int temp[])  
{  
    int i=first,m=mid;
    int j=mid+1,n=last;
    int k=0;
    while(i<=m && j<=n){
        if(a[i]<a[j]){
            temp[k++]=a[i];
            i++;
        }else{
            temp[k++]=a[j];
            j++;
        }
    }        
    while(i<=m){
            temp[k++]=a[i];
            i++;
    }
    while(j<=n){
        temp[k++]=a[j];
        j++;
    }
    // copy back to a
    for(int i=0;i<k;i++){
        a[first+i]=temp[i];
    }
}  
void mergesort(int a[], int first, int last, int temp[])  
{  
    if(first<last){
        int mid=(first+last)/2;
        mergesort(a,first,mid,temp);
        mergesort(a,mid+1,last,temp);
        mergearray(a, first, mid, last, temp);
    }
}  
  
int main()
{
        //测试
    int N = 10;
    int A[]={9,12,17,30,50,20,60,65,4,19};
    int B[]={9,12,17,30,50,4,20,60,65,70};
    int *temp=new int[N];
    
    mergesort(A,0,N-1,temp);
    print(temp,N);
    return 0;
}