归并排序思想,以及代码实现

将区间不断二等分,二等分…
然后一个接一个合并
假设merge_sort(int a[],int l,int r)
为 此次划分的区间为l到r,如何继续划分以及排序的问题

代码如下:

int a[N],temp[N];
void merge_sort(int a[],int l,int r){
	if(l>=r) return ;
	int mid=l+r>>1;
	
	// 划分区间,使得l到mid有序,mid+1到r有序	
	merge_sort(a,l,mid);
	merge_sort(a,mid+1,r);
	
	//现在考虑区间合并问题
	int k=0,i=l,j=mid+1;
	while(i<=mid&&j<=r)
		if(a[i]<=a[j]) temp[k++]=a[i++];
		else temp[k++]=a[j++];
	while(i<=mid) temp[k++]=a[i++];
	while(j<=r) temp[k++]=a[j++];
	
	for(i=l,j=0;i<=r;i++,j++) a[i]=temp[j];
}

Java代码实现:

 static private  void mergeSort(T[] arr, int l, int r, Comparator comparator,Object[] temp) {
        if (l >= r) return;
        int mid = l + r >> 1;

        mergeSort(arr, l, mid, comparator,temp);
        mergeSort(arr, mid + 1, r, comparator,temp);
        int k = 0, i = l, j = mid + 1;
        while (i <= mid && j <= r)
            if (comparator.compare(arr[i], arr[j]) <= 0) temp[k++] = arr[i++];
            else temp[k++] = arr[j++];
        while (i <= mid) temp[k++] = arr[i++];
        while (j <= r) temp[k++] = arr[j++];

        for (i = l, j = 0; i <= r; i++, j++) arr[i] = (T) temp[j];
    }