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

In this article 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 equals 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 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 to the index which 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 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 to the index which out of the vectors of pairs.

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

Program 1:

 `// 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 ` `    ``// lower_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
```

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