1.这段代码很简单，就是一个基本的归并排序，知道这个类中的sort实现归并排序就OK.
package 归并排序;import java.util.Arrays;public class SequentialMergeSort  {      public void sort(int[] arr) {        // handle null inputs        if (arr == null) {            throw new IllegalArgumentException("Input array cannot be null");        }        if (arr.length == 0 || arr.length == 1) {            // already sorted return            return;        }        int start = 0;        int end = arr.length - 1;        mergeSort(arr, start, end);    }    // helper method for merge sort    protected void mergeSort(int[] arr, int start, int end) {        if (start < end) {            int mid = (start + end) / 2;            mergeSort(arr, start, mid);            mergeSort(arr, mid + 1, end);            merge(arr, start, mid, end);        }    }    protected void merge(int[] arr, int start, int mid, int end) {        // copy the left half into left array        int[] leftArray = Arrays.copyOfRange(arr, start, mid + 1);        // copy right half into right array        int[] rightArray = Arrays.copyOfRange(arr, mid + 1, end + 1);        int leftArrayPtr = 0, rightArrayPtr = 0, inputArrayPtr = start;        // merge until we reach end of either one of the arrays        for (; leftArrayPtr < leftArray.length && rightArrayPtr < rightArray.length; inputArrayPtr++) {            if (leftArray[leftArrayPtr] <= rightArray[rightArrayPtr]) {                arr[inputArrayPtr] = leftArray[leftArrayPtr];                leftArrayPtr++;            } else {                arr[inputArrayPtr] = rightArray[rightArrayPtr];                rightArrayPtr++;            }        }        // finish up if there are any remaining elements        for (; leftArrayPtr < leftArray.length; leftArrayPtr++, inputArrayPtr++) {            arr[inputArrayPtr] = leftArray[leftArrayPtr];        }        for (; rightArrayPtr < rightArray.length; rightArrayPtr++, inputArrayPtr++) {            arr[inputArrayPtr] = rightArray[rightArrayPtr];        }    }}