归并排序

//归并排序
    public int[] mergeSort(int[] a, int low, int high) {
        int mid = (low+high) / 2;
        if (low < high) {
            mergeSort(a, low, mid);
            mergeSort(a, mid+1, high);
            merge(a, low, mid, high);
        }
        return a;
    }
    private void merge(int[] a, int low, int mid, int high) {
        int[] temp = new int[high-low+1];
        int i = low;
        int j = mid + 1;
        int k = 0;
        while (i <= mid && j<=high) {
            if (a[i] < a[j]) {
                temp[k++] = a[i++];
            } else {
                temp[k++] = a[j++];
            }
        }

        while (i<=mid) {
            temp[k++] = a[i++];
        }

        while (j<=high) {
            temp[k++] = a[j++];
        }

        for(int x = 0; x<temp.length; x++) {
            a[x+low] = temp[x];
        }
    }