归并排序java

**原理：归并排序就是将一个数组分成两个子数组，将两个子数组分成四个子数组，直到每个数组拆分成一个一个 在将其进行归并
**

在这里插入代码片/**
 * ClassName: Code4_mergeSort
 * Package: PACKAGE_NAME
 * Description:
 *
 * @Author yang shen
 * @Create 2024/1/17 10:35
 * @Version 1.0
 */
public class Code4_mergeSort {

    public static void mergeSort(int[] arr) {
        if (arr == null || arr.length < 2) return;
        mergeSort(arr, 0, arr.length - 1);
    }


    public static void mergeSort(int[] arr, int l, int r) {
        if (l == r) return;
        int mid = l + ((r - l) >> 1);
        mergeSort(arr,l,mid);
        mergeSort(arr,mid + 1,r);
        merge(arr, l ,mid, r);
    }

    public static void merge(int[] arr, int l, int m, int r) {
        int[] help = new int[r - l + 1];
        int i = 0;
        int p1 = l;
        int p2 = m + 1;

        while (p1 <= m && p2 <= r) {
            help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
        }

        while (p1 <= m) {
            help[i++] = arr[p1++];
        }

        while (p2 <= r) {
            help[i++] = arr[p2++];
        }

        for (int j = 0; j < help.length; j++) {
            arr[l + j] = help[j];
        }

    }

    public static void printArray(int[] arr) {
        for(int num : arr) {
            System.out.print(num + " ");
        }
        System.out.println();
    }


    public static void main(String[] args) {

        int[] arr = {5,2,3,1,4};
        mergeSort(arr);
        printArray(arr);

    }

}