二分查找练习

#include <stdio.h>
/*非递归二分*/
int HalfSearch(int a[], int low, int high, int key)
{
    while(low <= high)
    {
        int mid = (low + high) / 2;
        if(a[mid] > key)
        {
            high = mid - 1;
        }
        else if(a[mid] < key)
        {
            low = mid + 1;
        }
        else
        {
            return mid;
        }
    }
}
/*递归二分*/
int HalfSearch2(int a[], int low, int high, int key)
{
    int mid = (low + high) / 2;
    if (low >= high)
    {
        return mid;
    }
    if (a[mid] > key) mid = HalfSearch2(a, low, mid - 1, key);
    else if(a[mid] < key) mid = HalfSearch2(a, mid + 1, high, key);
}

/*找到第一个等于key的下标*/
int HalfSearch3(int a[], int low, int high, int key)
{
    while(low <= high)
    {
        int mid = (low + high) / 2;
        if(a[mid] > key)
        {
            high = mid - 1;
        }
        else if(a[mid] < key)
        {
            low = mid + 1;
        }
        else
        {
            if ((0 == mid) || (a[mid - 1] != key))
            {
                return mid;
            }
            else
            {
                high = mid - 1;
            }
        }
    }
}

/*找到最后一个等于key的下标*/
int HalfSearch4(int a[], int low, int high, int key)
{
    int n = high;
    while(low <= high)
    {
        int mid = (low + high) / 2;
        if(a[mid] > key)
        {
            high = mid - 1;
        }
        else if(a[mid] < key)
        {
            low = mid + 1;
        }
        else
        {
            if ((n == mid) || (a[mid + 1] != key))
            {
                return mid;
            }
            else
            {
                low = mid + 1;
            }
        }
    }
}

/*找到第一个大于或等于key的下标*/
int HalfSearch5(int a[], int low, int high, int key)
{
    while(low <= high)
    {
        int mid = (low + high) / 2;
        if(a[mid] >= key)
        {
            if ((0 == mid) || (a[mid - 1] < key))
            {
                return mid;
            }
            else
            {
                high = mid - 1;
            }
        }
        else if(a[mid] < key)
        {
            low = mid + 1;
        }
    }
}

/*找到最后一个小于或等于key的下标*/
int HalfSearch6(int a[], int low, int high, int key)
{
    int n = high;
    while(low <= high)
    {
        int mid = (low + high) / 2;
        if(a[mid] >= key)
        {
            high = mid - 1;
        }
        else if(a[mid] <= key)
        {
            if ((n == mid) || (a[mid + 1] > key))
            {
                return mid;
            }
            else
            {
                low = mid + 1;
            }
        }
    }
}

int main()
{
    int i = 0;
    int a[10] = {2, 9, 4, 1, 3, 55, 46, 15, 10, 32};
    int b[10] = {1, 22, 30, 30, 30, 56, 60, 60, 90, 91};
    // for (i = 0; i < 10; i++)
    // {
        // printf("a[%d]:%d
", i, a[i]);
    // }s
    printf("%d
", HalfSearch6(b, 0, 9, 50));
    return 0;
}