分治算法-二分查找

二分查找：

int binary_search_recursion(const int array[], int low, int high, int key)
{
    int mid = low + (high - low)/2;
    if(low > high)
        return -1;
    else{
        if(array[mid] == key)
            return mid;
        else if(array[mid] > key)
            return binary_search_recursion(array, low, mid-1, key);
        else
            return binary_search_recursion(array, mid+1, high, key);
    }
}

int binary_search_loop(const int array[], int len, int key)
{
    int low = 0;
    int high = len - 1;
    int mid;
    while(low <= high){
        mid = (low+high) / 2;
        if(array[mid] == key)
            return mid;
        else if(array[mid] > key)
            high = mid - 1;
        else
            low = mid + 1;
    }
    return -1;
}