Related Articles

# Rank of an element in a stream

• Difficulty Level : Medium
• Last Updated : 01 Jul, 2021

Given a stream of integers, lookup the rank of a given integer x. Rank of an integer in-stream is “Total number of elements less than or equal to x (not including x)”.
If an element is not found in the stream or is smallest in stream, return -1.
Examples:

```Input :  arr[] = {10, 20, 15, 3, 4, 4, 1}
x = 4;
Output : Rank of 4 in stream is: 3
There are total three elements less than
or equal to x (and not including x)

Input : arr[] = {5, 1, 14, 4, 15, 9, 7, 20, 11},
x = 20;
Output : Rank of 20 in stream is: 8```

A relatively easy way to implement this is to use an array that holds all the elements in sorted order. When a new element is inserted we would shift the elements. Then we perform binary search on the array to get the right-most index of x and return that index. getRank(x) would work in O(log n) but insertion would be costly.
An efficient way is to use a Binary Search Tree. Each Node will hold the data value and size of its left subtree.
We traverse the tree from root and compare the root values to x.

1. If root->data == x, return size of left subtree of root.
2. If x < root->data, return getRank(root->left)
3. If x > root->data, return getRank(root->right) + size of leftSubtree + 1.

Below is the solution.

## C++

 `// CPP program to find rank of an``// element in a stream.``#include ``using` `namespace` `std;` `struct` `Node {``    ``int` `data;``    ``Node *left, *right;``    ``int` `leftSize;``};` `Node* newNode(``int` `data)``{``    ``Node *temp = ``new` `Node;``    ``temp->data = data;``    ``temp->left = temp->right = NULL;``    ``temp->leftSize = 0;``    ``return` `temp;``}` `// Inserting a new Node.``Node* insert(Node*& root, ``int` `data)``{``    ``if` `(!root)``        ``return` `newNode(data);` `    ``// Updating size of left subtree.``    ``if` `(data <= root->data) {``        ``root->left = insert(root->left, data);``        ``root->leftSize++;``    ``}``    ``else``        ``root->right = insert(root->right, data);` `    ``return` `root;``}` `// Function to get Rank of a Node x.``int` `getRank(Node* root, ``int` `x)``{``    ``// Step 1.``    ``if` `(root->data == x)``        ``return` `root->leftSize;` `    ``// Step 2.``    ``if` `(x < root->data) {``        ``if` `(!root->left)``            ``return` `-1;``        ``else``            ``return` `getRank(root->left, x);``    ``}` `    ``// Step 3.``    ``else` `{``        ``if` `(!root->right)``            ``return` `-1;``        ``else` `{``            ``int` `rightSize = getRank(root->right, x);``              ``if``(rightSize == -1 ) ``return` `-1;``            ``return` `root->leftSize + 1 + rightSize;``        ``}``    ``}``}` `// Driver code``int` `main()``{``    ``int` `arr[] = { 5, 1, 4, 4, 5, 9, 7, 13, 3 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);``    ``int` `x = 4;` `    ``Node* root = NULL;``    ``for` `(``int` `i = 0; i < n; i++)``        ``root = insert(root, arr[i]);` `    ``cout << ``"Rank of "` `<< x << ``" in stream is: "``         ``<< getRank(root, x) << endl;` `    ``x = 13;``    ``cout << ``"Rank of "` `<< x << ``" in stream is: "``         ``<< getRank(root, x) << endl;` `    ``x = 8;``    ``cout << ``"Rank of "` `<< x << ``" in stream is: "``         ``<< getRank(root, x) << endl;``    ``return` `0;``}`

## Java

 `// Java program to find rank of an``// element in a stream.``class` `GfG {` `static` `class` `Node {``    ``int` `data;``    ``Node left, right;``    ``int` `leftSize;``}` `static` `Node newNode(``int` `data)``{``    ``Node temp = ``new` `Node();``    ``temp.data = data;``    ``temp.left = ``null``;``    ``temp.right = ``null``;``    ``temp.leftSize = ``0``;``    ``return` `temp;``}` `// Inserting a new Node.``static` `Node insert(Node root, ``int` `data)``{``    ``if` `(root == ``null``)``        ``return` `newNode(data);` `    ``// Updating size of left subtree.``    ``if` `(data <= root.data) {``        ``root.left = insert(root.left, data);``        ``root.leftSize++;``    ``}``    ``else``        ``root.right = insert(root.right, data);` `    ``return` `root;``}` `// Function to get Rank of a Node x.``static` `int` `getRank(Node root, ``int` `x)``{``    ``// Step 1.``    ``if` `(root.data == x)``        ``return` `root.leftSize;` `    ``// Step 2.``    ``if` `(x < root.data) {``        ``if` `(root.left == ``null``)``            ``return` `-``1``;``        ``else``            ``return` `getRank(root.left, x);``    ``}` `    ``// Step 3.``    ``else` `{``        ``if` `(root.right == ``null``)``            ``return` `-``1``;``        ``else` `{``            ``int` `rightSize = getRank(root.right, x);``          ``if``(rightSize == -``1``) ``return` `-``1``;``            ``return` `root.leftSize + ``1` `+ rightSize;``        ``}``    ``}``}` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``int` `arr[] = { ``5``, ``1``, ``4``, ``4``, ``5``, ``9``, ``7``, ``13``, ``3` `};``    ``int` `n = arr.length;``    ``int` `x = ``4``;` `    ``Node root = ``null``;``    ``for` `(``int` `i = ``0``; i < n; i++)``        ``root = insert(root, arr[i]);` `    ``System.out.println(``"Rank of "` `+ x + ``" in stream is : "``+getRank(root, x));` `    ``x = ``13``;``    ``System.out.println(``"Rank of "` `+ x + ``" in stream is : "``+getRank(root, x));` `}``}`

## Python3

 `# Python3 program to find rank of an``# element in a stream.` `class` `newNode:``    ``def` `__init__(``self``, data):``        ``self``.data ``=` `data``        ``self``.left ``=` `self``.right ``=` `None``        ``self``.leftSize ``=` `0` `# Inserting a new Node.``def` `insert(root, data):``    ``if` `root ``is` `None``:``        ``return` `newNode(data)` `    ``# Updating size of left subtree.``    ``if` `data <``=` `root.data:``        ``root.left ``=` `insert(root.left, data)``        ``root.leftSize ``+``=` `1``    ``else``:``        ``root.right ``=` `insert(root.right, data)``    ``return` `root` `# Function to get Rank of a Node x.``def` `getRank(root, x):``    ` `    ``# Step 1.``    ``if` `root.data ``=``=` `x:``        ``return` `root.leftSize` `    ``# Step 2.``    ``if` `x < root.data:``        ``if` `root.left ``is` `None``:``            ``return` `-``1``        ``else``:``            ``return` `getRank(root.left, x)` `    ``# Step 3.``    ``else``:``        ``if` `root.right ``is` `None``:``            ``return` `-``1``        ``else``:``            ``rightSize ``=` `getRank(root.right, x)``            ``if` `rightSize ``=``=` `-``1``:``                ``# x not found in right sub tree, i.e. not found in stream``                ``return` `-``1``            ``else``:``                ``return` `root.leftSize ``+` `1` `+` `rightSize` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``arr ``=` `[``5``, ``1``, ``4``, ``4``, ``5``, ``9``, ``7``, ``13``, ``3``]``    ``n ``=` `len``(arr)``    ``x ``=` `4` `    ``root ``=` `None``    ``for` `i ``in` `range``(n):``        ``root ``=` `insert(root, arr[i])` `    ``print``(``"Rank of"``, x, ``"in stream is:"``,``                       ``getRank(root, x))``    ``x ``=` `13``    ``print``(``"Rank of"``, x, ``"in stream is:"``,``                       ``getRank(root, x))``    ``x ``=` `8``    ``print``(``"Rank of"``, x, ``"in stream is:"``,``                       ``getRank(root, x))``        ` `# This code is contributed by PranchalK`

## C#

 `// C# program to find rank of an``// element in a stream.``using` `System;``    ` `class` `GFG``{``public` `class` `Node``{``    ``public` `int` `data;``    ``public` `Node left, right;``    ``public` `int` `leftSize;``}` `static` `Node newNode(``int` `data)``{``    ``Node temp = ``new` `Node();``    ``temp.data = data;``    ``temp.left = ``null``;``    ``temp.right = ``null``;``    ``temp.leftSize = 0;``    ``return` `temp;``}` `// Inserting a new Node.``static` `Node insert(Node root, ``int` `data)``{``    ``if` `(root == ``null``)``        ``return` `newNode(data);` `    ``// Updating size of left subtree.``    ``if` `(data <= root.data)``    ``{``        ``root.left = insert(root.left, data);``        ``root.leftSize++;``    ``}``    ``else``        ``root.right = insert(root.right, data);` `    ``return` `root;``}` `// Function to get Rank of a Node x.``static` `int` `getRank(Node root, ``int` `x)``{``    ``// Step 1.``    ``if` `(root.data == x)``        ``return` `root.leftSize;` `    ``// Step 2.``    ``if` `(x < root.data)``    ``{``        ``if` `(root.left == ``null``)``            ``return` `-1;``        ``else``            ``return` `getRank(root.left, x);``    ``}` `    ``// Step 3.``    ``else``    ``{``        ``if` `(root.right == ``null``)``            ``return` `-1;``        ``else``        ``{``            ``int` `rightSize = getRank(root.right, x);``              ``if``(rightSize == -1) ``return` `-1;``            ``return` `root.leftSize + 1 + rightSize;``        ``}``    ``}``}` `// Driver code``public` `static` `void` `Main(String[] args)``{``    ``int` `[]arr = { 5, 1, 4, 4, 5, 9, 7, 13, 3 };``    ``int` `n = arr.Length;``    ``int` `x = 4;` `    ``Node root = ``null``;``    ``for` `(``int` `i = 0; i < n; i++)``        ``root = insert(root, arr[i]);` `    ``Console.WriteLine(``"Rank of "` `+ x +``                      ``" in stream is : "` `+``                      ``getRank(root, x));` `    ``x = 13;``    ``Console.WriteLine(``"Rank of "` `+ x +``                      ``" in stream is : "` `+``                      ``getRank(root, x));``}``}` `// This code is contributed by PrinciRaj1992`

## Javascript

 ``
Output

```Rank of 4 in stream is: 3
Rank of 13 in stream is: 8
Rank of 8 in stream is: -1```

Another approach:
Traverse the array from the beginning. While traversing, count the nodes which is equal to or less than the given key.Print the count(Rank).

## C++

 `// C++ program to find rank of an``// element in a stream.``#include ``using` `namespace` `std;` `// Driver code``int` `main()``{``    ``int` `a[] = {5, 1, 14, 4, 15, 9, 7, 20, 11};``    ``int` `key = 20;``    ``int` `arraySize = ``sizeof``(a)/``sizeof``(a[0]);``    ``int` `count = 0;``    ``for``(``int` `i = 0; i < arraySize; i++)``    ``{``        ``if``(a[i] <= key)``        ``{``            ``count += 1;``        ``}``    ``}``    ``cout << ``"Rank of "` `<< key << ``" in stream is: "``            ``<< count-1 << endl;``    ``return` `0;``}` `// This code is contributed by``// Ashwin Loganathan.`

## Java

 `// Java program to find rank of an``// element in a stream.``class` `GFG``{` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``int` `a[] = {``5``, ``1``, ``14``, ``4``, ``15``, ``9``, ``7``, ``20``, ``11``};``    ``int` `key = ``20``;``    ``int` `arraySize = a.length;``    ``int` `count = ``0``;``    ``for``(``int` `i = ``0``; i < arraySize; i++)``    ``{``        ``if``(a[i] <= key)``        ``{``            ``count += ``1``;``        ``}``    ``}``    ``System.out.println(``"Rank of "` `+ key +``                    ``" in stream is: "` `+ (count - ``1``));``}``}` `// This code has been contributed by 29AjayKumar`

## Python3

 `# Python3 program to find rank of an``# element in a stream.` `# Driver code``if` `__name__ ``=``=` `'__main__'``:``    ``a ``=` `[``5``, ``1``, ``14``, ``4``, ``15``,``            ``9``, ``7``, ``20``, ``11``]``    ``key ``=` `20``    ``arraySize ``=` `len``(a)``    ``count ``=` `0``    ``for` `i ``in` `range``(arraySize):``        ``if` `a[i] <``=` `key:``            ``count ``+``=` `1``            ` `    ``print``(``"Rank of"``, key,``          ``"in stream is:"``, count ``-` `1``)` `# This code is contributed by PranchalK`

## C#

 `// C# program to find rank of an``// element in a stream.``using` `System;` `class` `GFG``{``// Driver code``public` `static` `void` `Main()``{``    ``int` `[]a = {5, 1, 14, 4, 15, 9, 7, 20, 11};``    ``int` `key = 20;``    ``int` `arraySize = a.Length;``    ``int` `count = 0;``    ``for``(``int` `i = 0; i < arraySize; i++)``    ``{``        ``if``(a[i] <= key)``        ``{``            ``count += 1;``        ``}``    ``}``    ``Console.WriteLine(``"Rank of "` `+ key +``                      ``" in stream is: "` `+``                            ``(count - 1));``}``}` `// This code is contributed by``// Akanksha Rai`

## PHP

 ``

## Javascript

 ``

Output:

`Rank of 20 in stream is: 8`

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.

My Personal Notes arrow_drop_up