[算法导论]在一个数组中寻找最大值和最小值所需要进行比较的次数

数组大小为ArraySize，若ArraySize为偶数，则需要（n-2）/2×3+1次比较；若ArraySize位奇数，则需要(n-1）/2×3次比较。以两个数为一组，首先比较这两个的大小，然后分别与当前最小值和最大值比较。

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

#define MIN(a, b) ((a) < (b) ? (a) : (b))
#define MAX(a, b) ((a) > (b) ? (a) : (b))

#define GetMinAndMax(a, b, minimum, maximum, times) \
({ \
    unsigned int arg1 = (a); \
    unsigned int arg2 = (b); \
    (minimum) = MIN(arg1, arg2); \
    (maximum) = MAX(arg1, arg2); \
    (times)++; \
    printf("time %3d: Compared %3d and %3d\n", times, arg1, arg2); \
})

#define ARRAY_SIZE  99
static int _Array[ARRAY_SIZE];

static void InitArray(void)
{
    srand((unsigned int)time(NULL));
    for(int i = 0; i < ARRAY_SIZE; i++)
        _Array[i] = rand() % (ARRAY_SIZE * 10);

    return;
}

static void PrintArray(void)
{
    for(int i = 0; i < ARRAY_SIZE; i += 5)
    {
        printf("%d\t%d\t%d\t%d\t%d\n",
            _Array[i], _Array[i + 1], _Array[i + 2], _Array[i + 3], _Array[i + 4]);
    }

    return;
}

static void Findminimum(void)
{
    unsigned int times = 0;
    int minimum;
    int maximum;
    int beginIndex;
    int tempMinimum;
    int tempMaximum;

    if(ARRAY_SIZE % 2 == 0)
    {
        GetMinAndMax(_Array[0], _Array[1], minimum, maximum, times);
        beginIndex = 2;
    }
    else
    {
        minimum = maximum = _Array[0];
        beginIndex = 1;
    }

    for(int i = beginIndex; i < ARRAY_SIZE; i += 2)
    {
        GetMinAndMax(_Array[i], _Array[i + 1], tempMinimum, tempMaximum, times);
        GetMinAndMax(minimum, tempMinimum, minimum, tempMinimum, times);
        GetMinAndMax(tempMaximum, maximum, tempMaximum, maximum, times);
    }
    printf("Has compared %d times, and minimum is %d, maximum is %d\n", times, minimum, maximum);
}

int main(int argc, char * argv[])
{
    InitArray();
    PrintArray();
    Findminimum();

    return EXIT_SUCCESS;
}