"stl中upper_bound和lower_bound的区别"

Question

I was looking at how the upper_bound and lower_bound algorithms work in stl on these pages: lower_bound<\/a> , upper_bound<\/a> , and it's documented the same way on these pages: lower_bound<\/a> , upper_bound<\/a>

if (*it<val) {                 // or: if (comp(*it,val)), for version (2)

Answer 1

value a a a b b b c c c
index 0 1 2 3 4 5 6 7 8
bound       l     u

Where l represents the lower bound of b , and u represents the upper bound of b .

So if there are range of values that are "equal" with respect to the comparison being used, lower_bound gives you the first of this, upper_bound gives you one-past-the-end of these. This is the normal pattern of STL ranges [first, last) .

Answer 2

lower_bound :

Returns an iterator pointing to the first element in the range [first,last) which does not compare less than val .

upper_bound :

Returns an iterator pointing to the first element in the range [first,last) which compares greater than val.

Now there is a difference between being no less than something and greater than something.

For example, if you compare 4 and 5 , you can say that

5 is _not less than_ 4
5 is _greater than_  4

However if you compare you compare 4 and 4 :

4 is _not less than_    4
4 is _not greater than_ 4

Answer 3

A simple answer is and less confusing WAY to remember this is below

std::lower_bound - returns iterator to first element in the given range which is EQUAL_TO or Greater than val.

std::upper_bound - returns iterator to first element in the given range which is Greater than val .

Answer 4

A simple answer from vscode

lower_bound: find the first pos in which val could be inserted without changing the order

upper_bound: find last postion in which val could be inserted without changing the order

Answer 5

The simple answer is [ lower_bound, upper_bound )<\/strong>