# Implementation of lower_bound and upper_bound on Set of Pairs in C++

lower_bound() returns an iterator pointing to the first element in the range [first, last) which has a value greater than or equals to the given value “val”. But in set of Pairs lower_bound() for pair(x, y) will return an iterator pointing to the position of pair whose the first value is greater than or equals x and second value is greater than equals to y.
If the above-mentioned criteria are not met, then it returns an iterator which points to the last pair of the set container.

Syntax: There are two ways to use lower_bound():

setName.lower_bound({a, b})

lower_bound(setName.begin(), setName.end(), pair(a, b))

upper_bound() returns an iterator pointing to the first element in the range [first, last) which has a value greater than the given value “val”. But in set of Pairs upper_bound() for pair(x, y) will return an iterator pointing to the position of pair whose the first value is greater than x and second value is greater than y.
If the above-mentioned criteria are not met, then it returns an iterator which points to the last pair of the set container.

Syntax: There are two ways to use upper_bound():

setName.upper_bound({a, b})

upper_bound(setName.begin(), setName.end(), pair(a, b))

Below is the program to demonstrate lower_bound() and upper_bound() in set of pairs:

 `// C++ program to demonstrate lower_bound() ` `// and upper_bound() in set of Pairs ` ` `  `#include ` `using` `namespace` `std; ` ` `  `// Function to implement lower_bound() ` `void` `findLowerBound( ` `    ``set >& arr, ` `    ``pair<``int``, ``int``>& p) ` `{ ` ` `  `    ``// Given iterator points to the ` `    ``// lower_bound() of given pair ` `    ``auto` `low = lower_bound(arr.begin(), ` `                           ``arr.end(), p); ` ` `  `    ``cout << ``"lower_bound() for {1, 2}"` `         ``<< ``" is: {"` `<< (*low).first << ``", "` `         ``<< (*low).second << ``"}"` `<< endl; ` `} ` ` `  `// Function to implement upper_bound() ` `void` `findUpperBound( ` `    ``set >& arr, ` `    ``pair<``int``, ``int``>& p) ` `{ ` ` `  `    ``// Given iterator points to the ` `    ``// lower_bound() of given pair ` `    ``auto` `up = upper_bound(arr.begin(), ` `                          ``arr.end(), p); ` ` `  `    ``cout << ``"upper_bound() for {1, 2}"` `         ``<< ``" is: {"` `<< (*up).first << ``", "` `         ``<< (*up).second << ``"}"` `<< endl; ` `} ` ` `  `// Driver Code ` `int` `main() ` `{ ` ` `  `    ``// Given sorted vector of Pairs ` `    ``set > s; ` ` `  `    ``// Insert pairs in set ` `    ``s.insert(make_pair(1, 2)); ` `    ``s.insert(make_pair(2, 4)); ` `    ``s.insert(make_pair(3, 7)); ` `    ``s.insert(make_pair(8, 9)); ` ` `  `    ``// Given pair { 1, 2 } ` `    ``pair<``int``, ``int``> p = { 1, 2 }; ` ` `  `    ``// Function Call to find lower_bound ` `    ``// of pair p in arr ` `    ``findLowerBound(s, p); ` ` `  `    ``// Function Call to find upper_bound ` `    ``// of pair p in arr ` `    ``findUpperBound(s, p); ` ` `  `    ``return` `0; ` `} `

Output:

```lower_bound() for {1, 2} is: {1, 2}
upper_bound() for {1, 2} is: {2, 4}
```

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