C实现方法经典算法之归并排序

// =====================【归并排序】==================

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

#define NUM 20
int arr[NUM] = { 0 };
int arr_temp1[NUM] = { 0 };
int arr_temp2[NUM] = { 0 };

void init()
{
    time_t tm;
    time(&tm);
    srand((unsigned int)tm);

    int max_item = 100;
    for (int i = 0; i != NUM; i++)
        arr[i] = rand() % max_item;
}

void display(int * arr)
{
    for (int i = 0; i != NUM; i++)
        printf("%-10d",arr[i]);
    printf("n");
}

void merge(int low,int mid,int high)
{
    for (int ii = 0; ii != mid + 1 - low; ii++)
    {
        arr_temp1[ii] = arr[low + ii];
    }
    arr_temp1[mid + 1 - low] = INT_MAX;

    for (int ii = 0; ii != high - mid; ii++)
    {
        arr_temp2[ii] = arr[mid + 1 + ii];
    }
    arr_temp2[high - mid] = INT_MAX;

    int i = 0;
    int j = 0;
    for (int k = low; k != high + 1; k++)
    {       
        if (arr_temp1[i] < arr_temp2[j])
            arr[k] = arr_temp1[i++];
        else
            arr[k] = arr_temp2[j++];
    }
}

void mergeSort(int low,int high)
{
    if (low >= high)
        return;

    int mid = (low + high) / 2;
    mergeSort(low,mid);
    mergeSort(mid + 1,high);
    merge(low,mid,high);
}


void main()
{
    init();
    printf("归并排序前n");
    display(arr);

    mergeSort(0,NUM - 1);
    printf("归并排序后n");
    display(arr);
}