计数排序

//元素只能为正整数

#include <iostream>
using namespace std;

int Max(int *a,int length)
{
    int temp=-1000;
    for (int i=0;i<length;i++)
        if (temp<a[i])
            temp=a[i];
    return temp;
}

void counting_sort(int *a,int *b,int k,int length)
{
    int *c;
    c=(int*)malloc(sizeof(int)*(k+1));
    for (int i=0;i<=k;i++)
        c[i]=0;

    for (int j=0;j<length;j++)
        c[a[j]]=c[a[j]]+1;

    for (int i=1;i<=k;i++)
        c[i]=c[i]+c[i-1];

    for (int j=length-1;j>=0;j--)
    {
        b[c[a[j]]-1]=a[j];
        c[a[j]]=c[a[j]]-1;
    }
    free(c);
}

int main()
{
    int a[]={2,15,1,3,21,32,1,3,7};
    int length=sizeof(a)/sizeof(int);
    int *b;
    b=new int[length];
    counting_sort(a,b,Max(a,length),length);

    for (int i=0;i<length;i++)
        cout<<b[i]<<"";
    cout<<endl;

    system("pause");
    free(b);
    return 0;
}