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# K’th Smallest/Largest Element using STL

Given an array and a number k where k is smaller than size of array, we need to find the k’th smallest element in the given array. Examples:

```Input : arr[] = {7, 10, 4, 3, 20, 15}
k = 2
Output : 4
Smallest element is 3. Second smallest
is 4.

Input : arr[] = {7, 10, 4, 3, 3, 15}
k = 2
Output : 4
Even if there are more than one occurrences
of 3, answer should be 4.

Input :arr[] = {7, 10, 4, 3, 20, 15}
k = 4
Output : 10```

We use set in C++ STL. 1) Insert all elements into a set. 2) Traverse the set and print k-th element.

Implementation:

## C++

 `// STL based C++ program to find k-th smallest ` `// element. ` `#include ` `using` `namespace` `std; `   `int` `kthSmallest(``int` `arr[], ``int` `n, ``int` `k) ` `{ ` `// Insert all elements into the set ` `set<``int``> s; ` `for` `(``int` `i = 0; i < n; i++) ` `s.insert(arr[i]); `   `// Traverse set and print k-th element ` `auto` `it = s.begin(); ` `for` `(``int` `i = 0; i < k - 1; i++) ` `it++; ` `return` `*it; ` `} `   `int` `main() ` `{ ` `int` `arr[] = { 12, 3, 5, 7, 3, 19 }; ` `int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]), k = 2; ` `cout << ``"K'th smallest element is "` `<< kthSmallest(arr, n, k); ` `return` `0; ` `} `

## Java

 `import` `java.util.Set;` `import` `java.util.TreeSet;`   `public` `class` `KthSmallest {` `    ``public` `static` `int` `kthSmallest(``int``[] arr, ``int` `n, ``int` `k) {` `        ``// Insert all elements into the set` `        ``Set s = ``new` `TreeSet();` `        ``for` `(``int` `i = ``0``; i < n; i++) {` `            ``s.add(arr[i]);` `        ``}`   `        ``// Traverse set and print k-th element` `        ``int` `i = ``0``;` `        ``for` `(Integer num : s) {` `            ``if` `(i == k - ``1``) {` `                ``return` `num;` `            ``}` `            ``i++;` `        ``}` `        ``return` `-``1``;` `    ``}`   `    ``public` `static` `void` `main(String[] args) {` `        ``int``[] arr = {``12``, ``3``, ``5``, ``7``, ``3``, ``19``};` `        ``int` `n = arr.length, k = ``2``;` `        ``System.out.println(``"K'th smallest element is "` `+ kthSmallest(arr, n, k));` `    ``}` `}`

## Python3

 `# STL based python program to find k-th smallest ` `# element. ` `from` `sortedcontainers ``import` `SortedList, SortedSet, SortedDict`   `def` `kthSmallest(arr, n, k) :` `    ``# Insert all elements into the set ` `    ``s``=``SortedSet(); ` `    ``for` `i ``in` `range``(``0``,n): ` `        ``s.add(arr[i]); ` `    `  `    ``# Traverse set and print k-th element ` `    ``i``=``1``;` `    ``ans``=``-``1``;` `    ``for` `val ``in` `s:` `        ``if``(i``=``=``k):` `            ``ans``=``val;` `            ``break``;` `        ``i``+``=``1``;`   `    ``return` `ans; `   `arr ``=` `[ ``12``, ``3``, ``5``, ``7``, ``3``, ``19` `]; ` `n ``=` `len``(arr);` `k ``=` `2``; ` `print``(``"K'th smallest element is "``,kthSmallest(arr, n, k)); `

## C#

 `using` `System;` `using` `System.Linq;` `using` `System.Collections.Generic;`   `class` `KthSmallest` `{` `    ``public` `static` `int` `kthSmallest(``int``[] arr, ``int` `k)` `    ``{` `        ``// Insert all elements into the set` `        ``var` `s = ``new` `SortedSet<``int``>(arr);`   `        ``// Traverse set and print k-th element` `        ``return` `s.ElementAt(k - 1);` `    ``}`   `    ``public` `static` `void` `Main(``string``[] args)` `    ``{` `        ``int``[] arr = { 12, 3, 5, 7, 3, 19 };` `        ``int` `k = 2;` `        ``Console.WriteLine(``"K'th smallest element is "` `+ kthSmallest(arr, k));` `    ``}` `}`

## Javascript

 `// Javascript program to find k-th smallest element. `   `function` `kthSmallest(arr, n, k) ` `{ ` `// Insert all elements into the set ` `    ``let s= ``new` `Set(); ` `    ``for` `(let i = 0; i < n; i++) ` `    ``s.add(arr[i]); ` `    `  `    ``// Traverse set and print k-th element ` `    ``let i = 0; ` `    ``for` `(const entry of s.values()) ` `    ``{` `        ``if``(i==k)` `        ``{` `            ``i=entry;` `            ``break``;` `        ``}` `        ``i++;` `    ``}` `        `  `    ``return` `i; ` `} `   `let arr = [ 12, 3, 5, 7, 3, 19 ]; ` `let n = arr.length, k = 2; ` `document.write(``"K'th smallest element is "``+ kthSmallest(arr, n, k));`

Output

`K'th smallest element is 5`

Time complexity: O(n Log n). Note that set in STL uses a self-balancing BST internally and therefore time complexity of search and insert operations is O(log n).
Auxiliary Space: O(n) where n is size of array, since n extra space has been taken.

This article is contributed by Roshan Halwai. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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