归并排序

public class MergeSort {
    public static void main(String[] args) {
//     int[] arr={8,2,7,4,5,3,6,1,0};
        int []arr = new int[80000000];
        for (int i = 0; i < 80000000; i++) {
            arr[i] = (int) (Math.random() * 8000000);
        }
        int[] temp =new int[arr.length];
        long start= System.currentTimeMillis();
        mergeSort(arr,0,arr.length-1,temp);
        long end= System.currentTimeMillis();
        System.out.println("time="+(end-start));
//         mergeSort(arr,0,arr.length-1,temp);
//        System.out.println(Arrays.toString(arr));
    }
    public static void mergeSort(int[] arr, int left, int right, int[] temp) {
        if(left < right) {
            int mid = (left + right) / 2;
            //递归分解
            mergeSort(arr, left, mid, temp);
            mergeSort(arr, mid + 1, right, temp);
            //递归合并
            merge(arr, left, mid, right, temp);
        }
    }
    public static void merge(int[] arr, int left, int mid, int right, int[] temp) {
        int i = left;
        int j = mid + 1;
        int t = 0;
        while (i <= mid && j <= right) {
            if (arr[i] <= arr[j]) {
                temp[t] = arr[i];
                t += 1;
                i += 1;
            } else {
                temp[t] = arr[j];
                t += 1;
                j += 1;
            }
        }
        //剩余的数继续插入到temp中
        while (i <= mid) {
            temp[t] = arr[i];
            t += 1;
            i += 1;
        }
          //剩余的数继续插入到temp中
        while (j <= right) {
            temp[t] = arr[j];
            t += 1;
            j += 1;
        }
        //合并
        t = 0;
        int tempLeft = left;
        while (tempLeft <= right) {
            arr[tempLeft] = temp[t];
            t += 1;
            tempLeft += 1;
        }
    }
}