归并排序

分而治之，归并排序

算法简单易懂，第一次编写错误，误把原数组下表当做临时数组考虑，结果可想而知，访问越界

下面是正确代码

import java.util.Scanner;

public class MergeSort {

	/**
	 * @param args
	 */
	public static void main(String[] args) 
	{
		// TODO Auto-generated method stub
		Scanner scanner=new Scanner(System.in);
		int  n=Integer.parseInt(scanner.next());;
		int []a=new int[n];
		for (int i = 0; i < n; i++)
			a[i]=Integer.parseInt(scanner.next());

		mergeSort(a,0,n-1);
		for (int i = 0; i < n; i++) 
			System.out.print(a[i]+"  ");
	}

	public static void mergeSort(int a[], int begin, int end) 
	{
		if ((end-begin)>=1) {
			mergeSort(a, begin, begin+(end-begin)/2);
			mergeSort(a, begin+(end-begin)/2+1, end);
			merge(a, begin, begin+(end-begin)/2, end);
		}
	}
	
	public static void merge(int a[], int b, int m, int e)
	{
		int []arry1=new int[m-b+1]; //temporary array
		int []arry2=new int[e-m];
		int i=b;
		int j=m+1;
		int k=0;
		for ( k = 0; k < arry1.length;) 
			arry1[k++]=a[i++];
		for ( k = 0; k < arry2.length;) 
			arry2[k++]=a[j++];

		i=0;
		j=0;
		for ( k = b; i<arry1.length&&j<arry2.length; k++)
			if(arry1[i]<arry2[j])	

				a[k]=arry1[i++];

			else

				a[k]=arry2[j++];

		while( i<arry1.length) 
				a[k++]=arry1[i++];
		while( j<arry2.length)
			a[k++]=arry2[j++];
}

#include <iostream>
using namespace std;

void merge(int a[],int p,int e,int m)
{
	int *la= new int [m-p+1];
	int *ra= new int [e-m];
	int j=0;
	int k=0;
	int i=0;
	for (i = p; i <= m; i++)
		la[i-p]=a[i];
	for (i = m+1; i <= e; i++)
		ra[i-m-1]=a[i];

	for (i= p; j<m-p+1&&k<e-m;i++)
		if (la[j]<ra[k])
			a[i]=la[j++];
		else
			a[i]=ra[k++];
	while (j<m-p+1)
		a[i++]=la[j++];
	while (k<e-m)
		a[i++]=ra[k++];
}

void mergesort(int a[], int p,int e)
{
	int q=(p+e)/2;
	if (e-1>=p)
	{	
		mergesort(a,p,q);
		mergesort(a,q+1,e);
		merge(a,p,e,q);
	}
}

int main(void)
{
	const int n=10;
	int a[n]={2,3,1,4,0,5,8,9,7,6};
	mergesort(a,0,n-1);
	for (int i = 0; i <n; i++)
		cout<<a[i]<<" ";
	cout<<endl;
}