MergeSort 归并排序

实现：

二路归并

public class TestMergeSort {

    public int[] mergeSortArray(int[] arr, int left, int right){
        if(left >= right) return null;

        int mid = (left+right)/2;
        mergeSortArray(arr, left, mid);
        mergeSortArray(arr, mid+1, right);

        merge(arr, left, mid, right);
        return arr;
    }

    public int[] merge(int[] arr, int left, int mid,  int right){
        int[] temp = new int[arr.length];
        int r1 = mid +1;
        int tIndex = left;
        int cIndex = left;

        while(left<=mid && r1<=right){
            if(arr[left] <= arr[r1]){
                temp[tIndex++] = arr[left++];
            }else{
                temp[tIndex++] = arr[r1++];
            }
        }

        while(left <= mid){
            temp[tIndex++] = arr[left++];
        }

        while(r1<=right){
            temp[tIndex++] = arr[r1++];
        }

        while(cIndex <= right){
            arr[cIndex] = temp[cIndex];
            cIndex++;
        }

        return arr;
    }

    public static void main(String[] args) {
        int[] arr = {6,2,4,1,5,9};
        TestMergeSort test = new TestMergeSort();
        test.mergeSortArray(arr, 0, arr.length -1);

        for(int i = 0 ; i < arr.length; i ++){
            System.out.println(arr[i]);
        }
    }

}

这个哥哥讲的不错，跟他学习了：

http://www.cnblogs.com/shudonghe/archive/2013/09/05/3302888.html

这个可以看看：

http://www.cnblogs.com/luweiseu/archive/2012/07/14/2591653.html