计数排序 C++代码

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>        //计数排序 
using namespace std;
int GetMax(int a[],int n)
{
	int max=a[0];
	for(int i=1;i<n;i++){
		if(a[i]>max)   max = a[i];
	}
	return max;
}
void countsort(int a[],int n)
{
	int m = GetMax(a,n);
	int b[m+1]={0};
	for(int j=0;j<n;j++)   b[a[j]]++;
	for(int i=0,k=0;i<=m||k<n;i++)
	{
		while(b[i]>0){
			a[k++] = i;
			b[i]--;
		}
	} 
} 
int main()
{
	int a[30] = {1,3,5,7,8,10,12,11,19,8,15,13,12,17,2,4,6,8,9,10,11,19,18,13,12,54,32,11,56,21};
	cout<<"before sort"<<endl;
	for(int i =0 ;i<30;i++) cout<<a[i]<<" ";
	cout<<endl;
	countsort(a,30);
	for(int i=0;i<30;i++)    cout<<a[i]<<" ";
	
	
	/*int b[21]={0};
	for(int i =0;i<25;i++)    b[a[i]]++;
	for(int j=0;j<=20;j++)
	{
		while(b[j]>0){
			cout<<j<<" ";
			b[j]--;
		}
	}  */
	return 0;
}