排序_归并排序_递归

Posted 2020-10-18 S-Mustard

public class DArray {
    private long a[];
    private int nElems;
    public DArray(int maxSize) {
        a=new long[maxSize];
        nElems=0;
    }
    //插入
        public void insert(long value) {
            a[nElems++]=value;
        }
        //显示
        public void display() {
            for(int j=0;j<nElems;j++)
                System.out.print(a[j]+" ");
            System.out.println();
        }
        public void mergeSort() {
            long[] workSpace=new long[nElems];
            recMergeSort(workSpace, 0, nElems-1);
        }
        private void recMergeSort(long[] workSpace,int lowerBound,int upperBound) {
            if(lowerBound==upperBound)
                return;
            else {
                int mid=(lowerBound+upperBound)/2;
                recMergeSort(workSpace, lowerBound, mid);
                recMergeSort(workSpace, mid+1, upperBound);
                merge(workSpace,lowerBound,mid+1,upperBound);//归并
            }
        }
        private void merge(long[] wordSpace, int lowerPtr, int hightPtr, int upperBound) {
            int j=0;
            int lowerBound=lowerPtr;
            int mid=hightPtr-1;
            int n=upperBound-lowerBound+1;//需要归并的数量
            while(lowerPtr<=mid && hightPtr<=upperBound) {
                if(a[lowerPtr]<a[hightPtr])
                    wordSpace[j++]=a[lowerPtr++];
                else
                    wordSpace[j++]=a[hightPtr++];
            }//取数组中最小的值放入临时数组中
            /*
             *  4 7 8  10 || 3 5  20 50
             *  比较4 与 3，3最小，临时数组[3]
             *  比较4与5 ，4 最小 ，临时数组[3，4]
             *  7 8 10||5 20  50
             *  比较7 与 5,5最小，临时数组[3，4，5]
             *  比较7与 20，7最小。临时数组[3，4，5，7]
             *  比较8与20，8最小，临时数组[3，4，5，8]
             *  比较10与20，10最小，临时数组[3，4，5，8，10]
             *  剩下  ||20 50
             *  最小按顺序存入临时数组中
             */
            
            //有可能有一边有剩余，但是不知道哪一边，所以每一边都写
            while(lowerPtr<=mid)
                wordSpace[j++]=a[lowerPtr++];
            
            while(hightPtr<=upperBound)
                wordSpace[j++]=a[hightPtr++];
            
            for(j=0;j<n;j++) {
                a[lowerBound+j]=wordSpace[j];
            }
            
        }

}

public class Test {

    public static void main(String[] args) {
        int maxSize=100;
        DArray array=new DArray(maxSize);
        array.insert(77);
        array.insert(99);
        array.insert(44);
        array.insert(55);
        array.insert(22);
        array.insert(88);
        array.insert(11);
        array.insert(0);
        array.insert(66);
        array.insert(33);
        array.display();
        array.mergeSort();
        array.display();

    }

}