数据结构---二分查找算法

1. 请自行学习二分查找算法，并实现以下函数：

 - 1.1 在一个已排序的整型数组array中，假设已知array数组的元素个数为n，需要查找的关键值为key，要求在array数组中查找值为key的数字，并返回该数字在数组中对应的索引值。请设计并实现该函数。

#include<stdio.h>

int bsearch1(int *array,int key,int n)

{

    int low=0,high=n-1,mid;

    while(low<=high)

    {

        mid=(low+high)/2;

        if(array[mid]==key)

        {

            printf("find out the key and its index is %d\n",mid);

            return mid;

        }

        if(array[0]<array[n-1])

        {

            if( array[mid] > key )

                high = mid-1;

            else

                low = mid+1;

        }

        else

        {

            if(key<array[mid])

                low=mid+1;

            else

                high=mid-1;

        }       

    }

    printf("key is not in this array!\n");

    return -1;  

}

 - 1.2 在标准C库中，二分查找函数bsearch的原型如下：

void *bsearch(const void *key, const void *base, size_t nmemb,

                       size_t size, int (*compar)(const void *, const void *))

 

实现代码如下：

void*  bsearch2(const void *key, const void *base, size_t nmemb,size_t size, int (*compar)(const void *, const void *))

{

    size_t low=0,high=nmemb-1;

    size_t mid;

    void *p;

    int result;

    while(low <=high)

    {

        mid=(low+high) /2;

        p=(void*) ( (char*)base +mid *size);//注意char的使用，p point to mid；

        result=(*compar)(key,p);

        if(result==0)                                 

            return p;

        else if(result < 0)

            high=mid-1;

        else

            low=mid+1;

    }

 

    return NULL;

}

 

int compare(const void *a,const void *b )//compare的实现；

{

    return (*(int*)a-*(int*)b);

}  

int main()

{  

    int a[8]={1,3,4,7,9,10,14,16};

    int b[8]={16,14,10,9,7,4,3,1};

    int *q;

    bsearch1(a,3,8);

    bsearch1(b,3,8);

    q=(int*)bsearch2(&a[3],a,8,4,compare);

    printf("the key's index is %d\n",q-a);

    return 0;

} 

本文转自 曾永刚 51CTO博客，原文链接:http://blog.51cto.com/zyg0227/231860