归并排序

void merge1(int *a,int left,int mid,int right){
	int n1=mid-left+1;
	int n2=right-mid;
	int *arr1=new int[n1];
	int *arr2=new int[n2];
	for(int i=0;i<n1;i++)
		arr1[i]=a[left+i];
	for(int i=0;i<n2;i++)
		arr2[i]=a[mid+i+1];
	int i=0,j=0,k=left;
	while(i<n1&&j<n2){
		if(arr1[i]<arr2[j])
			a[k++]=arr1[i++];
		else
			a[k++]=arr2[j++];
	}	
	while(i<n1){
		a[k++]=arr1[i++];
	}
	while(j<n2){
		a[k++]=arr2[j++];
	}
}
void merge2(int *a,int left,int mid,int right){
	int i=left;
	int j=mid+1;
	int *temp=new int[right-left+1];
	int t=0;
	while(i<=mid&&j<=right)
		if(a[i]<=a[j])
			temp[t++]=a[i++];
		else
			temp[t++]=a[j++];
	while(i<=mid)
		temp[t++]=a[i++];
	while(j<=right)
		temp[t++]=a[j++];
	t=0;
	while(left<=right)
		a[left++]=temp[t++];
}

void mergeSort(int *a,int left,int right){
	if(left<right){
		int mid=(left+right)/2;
		mergeSort(a,left,mid);
		mergeSort(a,mid+1,right);
                merge1(a,left,mid,right);      
		//merge2(a,left,mid,right);
	} 
}