How do i sort pair like this for example :
Input :
1 99
2 100
1 100
3 400
2 101
output :
1 100
1 99
2 101
2 100
3 400
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1Do you know about `if` statements and comparison operators (e.g. `<`, `>`, `<=', `>=`, etc.)? – James Adkison Mar 03 '16 at 15:27
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Possible duplicate of [Sort a vector of pairs by first element then by second element of the pair in C++?](http://stackoverflow.com/questions/18029110/sort-a-vector-of-pairs-by-first-element-then-by-second-element-of-the-pair-in-c) – Ivan Aksamentov - Drop Mar 03 '16 at 15:28
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@Drop Doesn't that sort ascending for `first` and `second`? – James Adkison Mar 03 '16 at 15:30
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wait going paste it here – nff21 Mar 03 '16 at 15:30
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btw its not duplicate my question is different – nff21 Mar 03 '16 at 15:31
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@nff21 Yes, your question is significantly different. Unique and never been asked before. So using search is not even an option – Ivan Aksamentov - Drop Mar 03 '16 at 15:32
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do you even read my question properly ? – nff21 Mar 03 '16 at 15:35
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The answer is simple but we can't help you if you don't show us what you have tried. This community is not here to write code for you. Answer: sort on `first` by checking `<` and if `first` is equivalent then proceed to sort on `second` by checking `>` – James Adkison Mar 03 '16 at 15:37
1 Answers
2
Create a comparator and use the std::sort function.
struct Comp {
bool operator()(const std::pair<int, int> &a, const std::pair<int, int> &b) {
if (a.first != b.first) {
return a.first < b.first;
}
return a.second > b.second;
}
};
Then create an instance of the struct and pass it into std::sort.
Comp comp_functor;
std::sort(myVec.begin(), myVec.end(), comp_functor);
To do this you'd need to #include <algorithm>. Also note that std::sort does not guarantee stability so if you want stability use std::stable_sort.
NickLamp
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You shouldn't be enabling users that ask bad questions (i.e., that are off-topic), see [here](http://stackoverflow.com/help/on-topic), by answering them. – James Adkison Mar 03 '16 at 15:41
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As written, if `b.first` is greater than `a.first` it starts comparing on `second` ... – James Adkison Mar 03 '16 at 15:43
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I saw the comment chain above but decided to post anyway because I thought the user might benefit from learning about what a comparator is (I'm assuming he hasn't seen them before, otherwise this exercise would have been trivial for him). Although the way he worded his question wasn't good I still think he deserves a well thought out answer. – NickLamp Mar 03 '16 at 15:44