码海拾遗：二分查找

　　二分查找法（Binary Search）：在有序数组中查找某一特定元素位置的搜索算法

　　实现：

//递归二分查找
template <typename T>
int binarySearch(T *arr, int start, int end, T key)
{
    if (start > end)
        return -1;

    int mid = (start + end) / 2;
    if (arr[mid] < key)
        return binarySearch(arr, mid+1, end, key);
    else if (arr[mid] > key)
        return binarySearch(arr, start, mid-1, key);
    else
        return mid;
}

//非递归二分查找
template <typename T>
int binarySearch(T *arr, int arrSize, T key)
{
    if (NULL == arr || arrSize == 0)
        return -1;

    int start = 0;
    int end = arrSize - 1;
    int mid = 0;

    while (start <= end)
    {
        mid = (start + end) / 2;
        if (arr[mid] == key)
            return mid;
        else if (arr[mid] < key)
            start = mid + 1;
        else
            end = mid - 1; 
    }
    return -1;
}

template <typename T>
int change(T& a, T& b)
{
    T tmp = a;
    a = b;
    b = tmp;
    return 0;
}

template <typename T>
int sort(T* arr, int arrSize)
{
    if (NULL == arr || arrSize == 0)
        return -1;
    for (int i = 0; i < arrSize; ++i)
    {
        for (int j = 0; j < arrSize; ++j)
        {
            if (arr[i] < arr[j])
                change(arr[i], arr[j]);
            /*{
                int tmp = arr[i];
                arr[i] = arr[j];
                arr[j] = tmp;
            }*/
        }
    }
    return 0;
}