排序算法总结

1. 快排

2. 堆排序

3. 简单排序（冒泡排序、选择排序和插入排序）

代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define N 20

static void show(int *arr, int len)
{
    int index;
    for(index = 0; index < len; index++)
    {
        printf("%d ", arr[index]);
    }
    printf("
");
}

static void swap(int *left, int *right)
{
    int tmp = *left;
    *left = *right;
    *right = tmp;
}

/**
 * 选择排序思想：依次将未排序的数组中的最小数放入pos所在位置，pos从0至N-1
 * -->前N-1个数放好位置，最后一个数就不用管了
 */
static void select_sort(int *arr, int len)
{
    int pos,index;
    int min_index;
    for(pos = 0; pos < len - 1; pos++)
    {
        min_index = pos;
        for(index = pos + 1; index < len; index++)
        {
            if(arr[index] < arr[min_index])
                min_index = index;
        }
        if(min_index != pos)
        {
            swap(arr + pos, arr + min_index);
        }
    }
}

static void insert_sort(int *arr, int len)
{
    int pos,index;
    int key;
    for(pos = 1; pos < len; pos++)
    {
        key = arr[pos];
        for(index = pos - 1; index >= 0; index--)
        {
            if(key < arr[index])
            {
                arr[index+1] = arr[index];
            }else
            {
                break;
            }
        }
        arr[index+1] = key;
    }
}

static void bubble_sort(int *arr, int len)
{
    int pos,index;
    for(pos = 0; pos < len - 1; pos++)
    {
        for(index = 0; index < len - 1 - pos; index++)
        {
            if(arr[index] > arr[index + 1])
            {
                swap(arr + index, arr + index + 1);
            }
        }
    }
}

static void bubble_sort2(int *arr, int len)
{
    int left, right, index;
    left = 0;
    right = len - 1;

    while(left < right)
    {
        for(index = left; index < right; index++)
        {
            if(arr[index] > arr[index+1])
            {
                swap(arr+index, arr+index+1);
            }
        }
        right--;
        if(left == right)
        {
            break;
        }
        for(index = right; index > left; index--)
        {
            if(arr[index] < arr[index-1])
            {
                swap(arr + index, arr + index -1);
            }
        }
        left++;
    }
}

int main(int argc, char *argv[])
{
    int arr[N], index;
    srand(time(NULL));
    for(index = 0; index < N; index++)
    {
        arr[index] = rand()%100 + 1;
    }
    show(arr, N);
    bubble_sort2(arr, N);
    show(arr, N);
    system("pause");
    return 0;
}

4. 归并排序

示意图：

代码如下：

/**
 * 归并排序
 */

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define N 20

void merge(int arr[],int start,int mid,int end)
{
    int i,j,k;
    int n1 = mid - start + 1;
    int n2 = end - mid;
    int *left = (int *)malloc(sizeof(int) * n1);
    int *right = (int *)malloc(sizeof(int) * n2);

    for(i = 0; i < n1; i++)
        left[i] = arr[start + i];
    for(j = 0; j < n2; j++)
        right[j] = arr[mid+1+j];
    i = 0;
    j = 0;
    k = start;
    while(i < n1 && j < n2)
    {
        if(left[i] < right[j])
            arr[k++] = left[i++];
        else
            arr[k++] = right[j++];
    }
    while(i < n1)
        arr[k++] = left[i++];
    while(j < n2)
        arr[k++] = right[j++];
    free(left);
    free(right);
}

void sort(int arr[], int start, int end)
{
    int mid;
    if(start < end)
    {
        mid = (start + end) / 2;
        sort(arr, start, mid);
        sort(arr, mid+1, end);
        merge(arr,start,mid,end);
    }
}

int main(int argc, char * argv[])
{
    int i,a[N];
    srand(time(NULL));
    for(i = 0; i < N; i++)
        a[i] = rand() % 100;
    printf("归并排序：
");
    printf("before : ");
    for(i = 0; i < N; i++)
        printf("%-2d ",a[i]);
    printf("
");
    
    sort(a,0,N-1);
    
    printf("after  : ");
    for(i = 0; i < N; i++)
        printf("%-2d ",a[i]);
    printf("
");
    system("pause");
    return 0;
}

方法2：用数组名以及数组长度作参数。如此一来，与之前的排序算法参数就统一起来了。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

static void show(int *arr, int len)
{
    int index;
    for(index = 0; index < len; index++)
    {
        printf("%3d", arr[index]);
    }
    printf("
");
}

static void merge(int *arr, int len)
{
    
    int index,i,j;
    int n1 = len / 2;
    int n2 = len - n1;
    int *left  = (int*)calloc(n1, sizeof(int));
    int *right = (int*)calloc(n2, sizeof(int));
    i = j = 0;

    for(index = 0; index < n1; index++)
    {
        left[i++] = arr[index];
    }
    for(; index < len; index++)
    {
        right[j++] = arr[index];
    }
    
    index = i = j = 0;
    while(i < n1 && j < n2)
    {
        if(left[i] < right[j])
        {
            arr[index++] = left[i++];
        }else
        {
            arr[index++] = right[j++];
        }
    }
    while(i < n1)
    {
        arr[index++] = left[i++];
    }
    while(j < n2)
    {
        arr[index++] = right[j++];
    }
    
    free(left);
    free(right);
    left = right = NULL;
}

static void sort(int *arr, int len)
{
    int n;
    if(len == 1)
    {
        return;
    }else
    {
        n = len/2;
        sort(arr, n);
        sort(arr + n, len-n);
        merge(arr,len);
    }    
}

int main(int argc, char *argv[])
{
    int arr[20],i;
    srand(time(NULL));
    for(i = 0; i < 20; i++)
    {
        arr[i] = rand()%100;
    }
    
    show(arr,20);
    sort(arr, 20);
    show(arr,20);

    system("pause");
    return 0;
}