归并排序（递归）代码详解

 归并是先递归后排序，把数组递归的分成两部分然后归并排序。

思想：分治思想。

package com.mahai.sort;

import java.util.Scanner;

public class MergeUp {
	private static String[] aux;
	//TODO 排序第一步
	public static void sort(String[] a) {
		aux = new String[a.length];
		sort(a,0,a.length-1);
	}
	//TODO 排序第二步
	private static void sort(String[] a,int low,int hi) {
		if (hi <= low) return;//如果符合条件跳出此方法，然后继续执行下一条语句（也就是第二个sort分类方法）
		int mid = low + (hi-low)/2;
		sort(a, low, mid);
		sort(a, mid+1, hi);
		merge(a, low, mid, hi);
	}
	//TODO 归并   将a[low..mid]和a[mid+1..hi]归并
	public static void merge(String[] a,int low,int mid,int hi) {
		int i = low, j = mid+1;
		for (int j2 = low; j2 <= hi; j2++) 
			aux[j2] = a[j2];
		for (int j2 = low; j2 <= hi; j2++) 
			if(i > mid)						a[j2]=aux[j++];
			else if(j > hi)					a[j2]=aux[i++];
			else if(less(aux[j],aux[i]))	a[j2]=aux[j++];
			else							a[j2]=aux[i++];
	}
	//TODO 比较大小
	private static boolean less(String a, String b) {
		return a.hashCode()