gXa's blog

Lower_Bound And Upper_Bound
By gXa, history, 7 years ago, In English

Can lower_bound and upper_bound work with vector of pair<pair<int, int>, int> or nested pairs. I tried doing so but it is showing me error. So, how should we do that?

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7 years ago, # |
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Don`t now how to do this. But I can tell you a substitute for this.

Implement your own struct for this. Like :

struct p{
    int a;
    int b;
    int c;
};

Write down a less than operator a separate comparator for it.

This is my code. Have a look.

My code — https://pastebin.com/BMM8f21P

Although I am having a small problem and I will be really happy if a third person can help us both. Lower bound returns the same value if its present in the query range. But in my code if I am searching {1 , 2 , 3} in the vector of particular struct, I am not getting the desired result.

I even implemented an (==) operator for this struct but it was not helpful.

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    7 years ago, # ^ |
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    The biggest thing that stands out in your code is that if all of the elements of the 3-tuple are equal, you're not returning anything from your comparison functions, like operator< I believe that's UB in C++, or whatever it is it's not going to be fun behavior.

    Your compiler should really be warning about that, -Wall is good practice if you're not already using that.

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7 years ago, # |
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What error are you actually getting? It looks to me like it should just work.

For example this doesn't error for me (with --std=c++14 if it matters):

  vector<pair<pair<int, int>, int>> v;
  lower_bound(v.begin(), v.end(), make_pair(make_pair(2, 42), 5));
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7 years ago, # |
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I believe making a custom comparator will solve the problem!

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