二分查找只有要查的元素位于中间时才能成功

[sukekiyo]

如题，当查找别的位置上时都失败

template<typename Pointer, typename T>
bool _binary_search(Pointer first, Pointer last, const T& value)
{
	last -= 1;
	//std::cout << *last;
	while(first < last)   
	{
		Pointer middle = first + (last - first) / 2;
		if (value < *middle)
		{
			last = middle - 1;
		}
		else if(*middle < value)
		{
			first = middle + 1;
		}
		else
		{
			return true;   //value == *middle
		}
	}
	return false;
}

[downmooner]

last -= 1; 这里为什么-1呢?


while(first <= last)

[smaltdd]

Pointer middle = first + (last - first) / 2;


first 和last是表示位置的，怎么能给查询的对象赋值呢？

[icecools]

为什么要这句？
last -= 1;

[downmooner]

int a[10]={0,1,2,3,4,5,6,7,8,9};
bool find(int first,int end,int v)
{
	while (first<=end)
	{
		int temp=first+(end-first)/2;
		if (a[temp]==v)
		{
			return true;
		}
		else if (a[temp]<v)
		{
			end=temp-1;
		} 
		else
			first=temp+1;
	}
	return false;
}

[sukekiyo]

last指向区间最后一个元素的后面一个位置，现在明白了要改为 last += 1;

[sukekiyo]

刚刚还是弄错了

[bfhtian]

Pointer是指针吗，相加会产生什么结果？

[tangshuiling]

[Quote=引用楼主 sukekiyo 的帖子:]
如题，当查找别的位置上时都失败


C/C++ code
template<typename Pointer, typename T>
bool _binary_search(Pointer first, Pointer last, const T& value)
{
last -= 1;
//std::cout << *last;
while(first < last)
{
Pointer middle = first + (last - first) / 2;
if (value < *middle)
{
last = middle - 1;
}
else if(*middle …
[/Quote]
while(first < last) 改while(first<=last)
极有可能first==last时元素相等