How to use lower_bound ( ) on pair class?

#1

ref line 36

#2

@prateek_5 waise koi way nhi hota but alternative way hai:
There is a way without constructing a temporary pair. All one needs is to define operator< between the pair and the other type. To avoid messing up with global definition of operator< for pair and int, define it for a wrapper:

template
struct Wrapper
{
T value;
};

template
bool operator<(const std::pair<T, T> & x, Wrapper value) {
return x.first < value.value;
}
template

bool operator<(Wrapper value, const std::pair<T, T> & x) {
return value.value < x.first;
}

int main()
{
// NOTE: using std::less<>, instead of the default std::less<std::pair<int, int>>
std::set<std::pair<int, int>, std::less<>> s {{1,2}, {1,3}, {4,1}, {5,1}, {5,2}};
Wrapper x{2};
auto it = s.lower_bound(x);
This is an overkill for std::pair<int, int>, but for more complicated types like std::pair<int, MyFancyClass> it can be costly to construct the smallest possible object. Also, for infinite-precision numbers, no such value exists. In that case, one must resort to the above technique. For more complicated types, it may be possible to simply overload operator<, without using a wrapper.

Note that the overloaded operators must be consistent with each other. They must be subject to the same order of elements

#3

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