线性时间排序 Sorting in linear time O(n)

 Sorting In Linear Time 

之前尝试过很多的排序算法, 都是基于比较的排序算法(base on comparing)

Collection of algorithm for sorting (part one)

http://blog.csdn.net/cinmyheart/article/details/39268783

Collection of algorithm for sorting (part two)

http://blog.csdn.net/cinmyheart/article/details/39396651

Collection of algorithm for sorting (part three)

http://blog.csdn.net/cinmyheart/article/details/39413037

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时间复杂度为O(n)的Counting Sort 计数排序

这里给出两个语言实现的版本

C语言实现:

/*********************************************************
 Code writer : EOF
 Code date   : 2014.01.11
 Code file   : counting_sort.c
 e-mail      : jasonleaster@gmail.com

 Code description:
   Here is a implementation for counting sort.

   If you find something wrong with my code, please touch
me by e-mail.

*********************************************************/
#include <stdio.h>
#include <stdlib.h>

int counting_sort(int *num,int size)
{
    if(!num)
    {
        return -1;
    }

    int *p_buffer = (int*)malloc(sizeof(int)*size);

    //initialization
    int i = 0;
    for(i = 0; i < size; i++)
    {
        p_buffer[i] = 0;
    }

    //counting
    for(i = 0; i < size; i++)
    {
        p_buffer[num[i]] += 1;
    }

    //output from bigger element to smaller element
    int index = 0;
    for(index = i = size -1;i >= 0; i--)
    {
        while(p_buffer[i]-- > 0)
        {
            num[(size -1) - index] = i;
            index--;
        }
    }

    free(p_buffer);
    return 0;
}

int main()
{
    int array[] = {1,3,4,3,2,7,4,0};
    int size_array = sizeof(array)/sizeof(array[0]);

    int i = 0;
    printf("Before sorting:array[] = \n");
    for(i = 0; i < size_array; i++)
    {
        printf("\t%d",array[i]);
    }

    printf("\n");
    counting_sort(array,size_array);

    printf("After sorting:array[] = \n");
    for(i = 0; i < size_array; i++)
    {
        printf("\t%d",array[i]);
    }
    printf("\n");

    return 0;
}

Python实现:

"""
 Code writer : EOF
 Code date   : 2014.01.11
 Code file   : counting_sort.py
 e-mail      : jasonleaster@gmail.com

 Code description:
   Here is a implementation for counting sort.

   If you find something wrong with my code, please touch
me by e-mail.
"""

def counting_sort(array) :
    size = len(array)
    buf  = [0] * size
    
    for i in range(0, size) :
        buf[array[i]] += 1
     
    for index in range(size -1, 0, -1) :
        i = index
        while buf[i] > 0 :
            array[(size -1) - index] = i
            index  -= 1
            buf[i] -= 1

    return array

array = [1,3,4,3,2,7,4,0]

print "Befor sorting" ,array

sorted_ary = counting_sort(array)

print "After sorting", sorted_ary

radix sorting wait for updating ...

既不是向东,也不是向西,而是指向内心

线性时间排序 Sorting in linear time O(n)

原文：http://blog.csdn.net/cinmyheart/article/details/42612043