数据结构--递归实现归并排序

/*通过递归实现归并排序
 * 具有思路：将要排序的数组不断划分，直到只有一个元素的时候停止；
 * 这是递归的基准条件，返回进行排序。
 * 归并排序的时间复杂度：O(NlogN):考虑的是复制数据到workarr和workarr到arr的次数
 * 
 * */
public class MergeWithRecursion {
    static int items = 6;
    static int[] arr = {10,8,9,59,2,4};
    public static void main(String[] args) {
        display();
        mergeSort();
        display();

    }
    
    public static void mergeSort(){
        int[] workarr = new int[items];
        recMergeSort(workarr,0,items-1);
    }

    private static void recMergeSort(int[] workarr, int low, int high) {
        if(low == high){
            return;
        }
        else{
            int mid = (low + high) / 2;
            recMergeSort(workarr,low,mid);
            recMergeSort(workarr,mid+1,high);
            merge(workarr,low,mid+1,high);
        }
        
    }

    private static void merge(int[] workarr, int low, int mid, int high) {
        //workarr index
        int j = 0;
        int lowbound = low;
        int midindex = mid - 1;
        int n = high - lowbound + 1;
        //进行归并到工作区数组
        while(low <= midindex && mid <= high){
            if(arr[low] < arr[mid]){
                workarr[j++] = arr[low++];
            }
            else{
                workarr[j++] = arr[mid++];
            }
        }
        
        while(low <= midindex){
            workarr[j++] = arr[low++];
        }
        
        while(mid <= high){
            workarr[j++] = arr[mid++];
        }
        
        //将工作区部分有序的数组复制到原来的数组
        for(int i = 0; i < n;i++){
            arr[lowbound + i] = workarr[i];
        }
    }
    
    public static void display(){
        for(int i = 0; i < arr.length;i++){
            System.out.print(arr[i] + " ");
        }
        System.out.println();
    }

}