struct node{
int i, j, val;
};
set<node> A;
I insert many nodes in A. Now I want to get the lower_bound for some val = k. How do I use A.lower_bound() in this case?
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struct node{
int i, j, val;
};
set<node> A;
I insert many nodes in A. Now I want to get the lower_bound for some val = k. How do I use A.lower_bound() in this case?
Название |
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Auto comment: topic has been updated by rachitiitr (previous revision, new revision, compare).
You can define a custom comparator and then make queries like A.lower_bound({0,0,k}) for example.
Check this example for more clarification: http://ideone.com/xbUGBr
You have to define the comparison operator (<) if you want to be able to do lower_bound. I've always liked the
friend
feature of C++.when you use
A.lower_bound(dummy)
it will return iterator to the first node not less thandummy
so your struct should be something like this
be careful, the std::set does not has
==
operator, and it uses the<
operator to achieve the uniqueness. in other words, if you insert node a and the set wants to check a against node b to check if they are equal or not, it will do the following,if ( a < b )
=> false thenif ( b < a )
=> false, then it assume that they are equal.so if your operator does not consider some element in the struct in the < operator it might be the case that the set assume 2 elements are equal while they are not "that's why i used the 3 variables in my example for the < operator".