二路归并排序，利用递归，时间复杂度o(nlgn)

public class MergeSort {
    public void mergeSort(int[]data, int left, int right)
    {
        if(left >= right) return;
        int mid = (left + right)/2;
        mergeSort(data, left, mid);
        mergeSort(data, mid+1, right);
        merge(data, left, mid, right);
    }
    public void merge(int[]data, int left, int mid, int right)
    {
        int[] temp = new int[data.length];//临时数组
        int index = left;//临时数组的下标
        int tmp = left;//记录data的左下标
        int center = mid + 1;
        while(left <= mid && center <= right)
        {
            if(data[left] < data[center])
            {
                temp[index++] = data[left++];
            }
            else
            {
                temp[index++] = data[center++];
            }
        }
        while(left <= mid)
        {
            temp[index++] = data[left++];
        }
        while(center <= right)
        {
            temp[index++] = data[center++];
        }
        while(tmp <= right)//将临时数组拷贝到原数组
        {
            data[tmp] = temp[tmp++];
        }
    }

    public static void main(String[] args)
    {
        int[] data = {3, 1, 4, 5, 15, 2, 8};
        MergeSort ms = new MergeSort();
        ms.mergeSort(data, 0, 6);
        for (int i : data) {
            System.out.print(i+"\t");
        }
    }
}