折半查找法

    /** 
     * 折半查找又称二分查找,算法复杂度为O(log(n)),但缺点是要求 
     * 待查表为有序表,此算法充分利用了数组的有序性,采用分治策略 
     * 找出待查元素在数组中的位置,若数组中不存在该元素,则返回-1 
     */  
      
    #include <stdio.h>  
      
    int binary_search(int array[], int n, int data)  
    {  
        int low = 0, high = n - 1, mid;  
      
        while(high >= low)  
        {  
            mid = (low + high) / 2;  
      
            if(array[mid] == data)  
                return mid;  
            else if(array[mid] > data)  
                high = mid - 1;  
            else  
                low = mid + 1;  
        }  
        return -1;  
    }  
      
    main()  
    {  
        int array[] = {1, 5, 30, 41, 100, 101};  
        printf("%d\n", binary_search(array, 6, 101));  
        printf("%d\n", binary_search(array, 6, 2));  
    }  
      
    运行结果:  
    5  
    -1