# upper_bound and lower_bound for non increasing vector in c++

The lower_bound() and upper_bound() functions, by default works on non-decreasing array. The lower_bound() function finds iterator of first element that does not compare less to given element. The upper_bound() function returns iterator to the first element that is greater.

Given an array converting this to a non-increasing vector, applying the std:: upper_bound and std:: lower_bound function to the vector

For array sorted in a non-increasing array, lower_bound() finds iterator to the first element that does not compare greater than to given element. upper_bound() finds iterator to the first element that is smaller than the given element. We use greater() for this purpose.

 `// C++ program to demonstrate the working of lower_bound() ` `// and upper_bound() for array sorted in non-decreasing ` `// array, ` `#include ` `#include ` `#include ` ` `  `int` `main() ` `{ ` `    ``int` `unsorted = { 3, 3, 2, 1, 5, 5, 4, 3, 7, 8 }; ` `    ``std::vector<``int``> v(unsorted, unsorted + 10); ` ` `  `    ``// sorting vector in non increasing order. Vector ` `    ``// becomes {8, 7, 5, 5, 4, 3, 3, 3, 2, 1} ` `    ``std::sort(v.begin(), v.end(), std::greater<``int``>()); ` ` `  `    ``std::vector<``int``>::iterator low, up; ` `    ``low = std::lower_bound(v.begin(), v.end(), 3, std::greater<``int``>());          ` `    ``up = std::upper_bound(v.begin(), v.end(), 5, std::greater<``int``>());           ` ` `  `    ``std::cout << ``"lower_bound at position "` `<< (low - v.begin()) << ``'\n'``; ` `    ``std::cout << ``"upper_bound at position "` `<< (up - v.begin()) << ``'\n'``; ` ` `  `    ``return` `0; ` `} `

Output:

```lower_bound at position 5
upper_bound at position 4
```

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