# Implementation of lower_bound() and upper_bound() in Vector of Pairs in C++

Last Updated : 21 Jul, 2022

Here we will discuss the implementation of the lower_bound() and upper_bound() in vector of pairs

### lower_bound():

It returns an iterator pointing to the first element in the range [first, last) which has a value greater than or equal to the given value “val”. But in Vector of Pairs lower_bound() for pair(x, y) will return an iterator pointing to the position of pair whose

• first value is greater than
• first value is equal to  x and second value is greater than equals to y.

If the above-mentioned criteria are not met, then it returns an iterator to the index which is out of the vectors of pairs.

### upper_bound():

It 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 Vector of Pairs upper_bound() for pair(x, y) will return an iterator pointing to the position of the pair whose

• First value is equal to x and the second value is greater than y, or
• Whose first value is greater than x.

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

Program 1:

## CPP

 `// C++ program to demonstrate lower_bound()` `// and upper_bound() in Vectors of Pairs`   `#include ` `using` `namespace` `std;`   `// Function to implement lower_bound()` `void` `findLowerBound(vector >& 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 {2, 5}"` `         ``<< ``" is at index: "` `<< low - arr.begin() << endl;` `}`   `// Function to implement upper_bound()` `void` `findUpperBound(vector >& arr,` `                    ``pair<``int``, ``int``>& p)` `{` `    ``// Given iterator points to the` `    ``// upper_bound() of given pair` `    ``auto` `up = upper_bound(arr.begin(), arr.end(), p);`   `    ``cout << ``"upper_bound() for {2, 5}"` `         ``<< ``" is at index: "` `<< up - arr.begin() << endl;` `}`   `// Driver Code` `int` `main()` `{` `    ``// Given sorted vector of Pairs` `    ``vector > arr;` `    ``arr = { { 1, 3 }, { 1, 7 }, { 2, 4 },` `            ``{ 2, 5 }, { 3, 8 }, { 8, 6 } };`   `    ``// Given pair {2, 5}` `    ``pair<``int``, ``int``> p = { 2, 5 };`   `    ``// Function Call to find lower_bound` `    ``// of pair p in arr` `    ``findLowerBound(arr, p);`   `    ``// Function Call to find upper_bound` `    ``// of pair p in arr` `    ``findUpperBound(arr, p);`   `    ``return` `0;` `}`

Output

```lower_bound() for {2, 5} is at index: 3
upper_bound() for {2, 5} is at index: 4
```