2.3.1 归并排序(分治法)

灯神讲解视频:https://www.bilibili.com/video/av9982752?from=search&seid=389996237580366908

public class MergeSort {
    public void printArr(int arr[]){
        for (int i = 0; i < arr.length; i++) {
            System.out.printf(arr[i]+"\t");
        }
        System.out.println();
    }
    public void mergeSortInner(int arr[], int left, int middle, int right) {
        final int LEFT_SIZE = middle - left;
        final int RIGHT_SIZE = right - middle+1;
        int[] leftPart = new int[LEFT_SIZE];
        int[] rightPart = new int[RIGHT_SIZE];
        for (int i = left; i < middle; i++) {
            leftPart[i - left] = arr[i];
        }
        printArr(leftPart);
        for (int i = middle; i <= right; i++) {
            rightPart[i - middle] = arr[i];
        }

        printArr(rightPart);

        int l = 0;
        int r = 0;
        int t = left;

        while (l < LEFT_SIZE && r < RIGHT_SIZE) {
            if (leftPart[l] < rightPart[r]) {
                arr[t] = leftPart[l];
                l++;
                t++;
            } else {
                arr[t] = rightPart[r];
                r++;
                t++;
            }
        }

        printArr(arr);


        while (l<LEFT_SIZE){
            arr[t] = leftPart[l];
            l++;
            t++;
        }

        printArr(arr);


        while (r<RIGHT_SIZE){
            arr[t] = rightPart[r];
            r++;
            t++;
        }


    }

    public void mergeSort(int arr[],int left,int right) {
        if (left == right){
            return;
        }else{
            int middle = (left+right)/2;
            mergeSort(arr,left,middle);
            mergeSort(arr,middle+1,right);
            mergeSortInner(arr,left,middle+1,right);
        }
    }

    public static void main(String[] args) {
        int arr[] = {
   
   2,8,9,10,4,5,6,7};
        int l = 0;
        int r = arr.length-1;
        int m = 4;
        new MergeSort().mergeSort(arr,l,r);
        for (int i = 0; i < arr.length; i++) {
            System.out.printf(arr[i]+"\t");
        }
    }
}