Related Articles

# Print levels with odd number of nodes and even number of nodes

• Last Updated : 28 Jun, 2021

Given an N-ary tree, print all the levels with odd and even number of nodes in it.

Examples

```For example consider the following tree
1               - Level 1
/     \
2       3           - Level 2
/   \       \
4     5       6        - Level 3
/  \     /
7    8   9         - Level 4

The levels with odd number of nodes are: 1 3 4
The levels with even number of nodes are: 2```

Note: The level numbers starts from 1. That is, the root node is at the level 1.

Approach

• Insert all the connecting nodes to a 2-D vector tree.
• Run a DFS on the tree such that height[node] = 1 + height[parent]
• Once DFS traversal is completed, increase the count[] array by 1, for every node’s level.
• Iterate from first level to last level, and print all nodes with count[] values as odd to get level with odd number nodes.
• Iterate from first level to last level, and print all nodes with count[] values as even to get level with even number nodes.

Below is the implementation of the above approach:

## C++

 `// C++ program to print all levels``// with odd and even number of nodes` `#include ``using` `namespace` `std;` `// Function for DFS in a tree``void` `dfs(``int` `node, ``int` `parent, ``int` `height[], ``int` `vis[],``         ``vector<``int``> tree[])``{``    ``// calculate the level of every node``    ``height[node] = 1 + height[parent];` `    ``// mark every node as visited``    ``vis[node] = 1;` `    ``// iterate in the subtree``    ``for` `(``auto` `it : tree[node]) {` `        ``// if the node is not visited``        ``if` `(!vis[it]) {` `            ``// call the dfs function``            ``dfs(it, node, height, vis, tree);``        ``}``    ``}``}` `// Function to insert edges``void` `insertEdges(``int` `x, ``int` `y, vector<``int``> tree[])``{``    ``tree[x].push_back(y);``    ``tree[y].push_back(x);``}` `// Function to print all levels``void` `printLevelsOddEven(``int` `N, ``int` `vis[], ``int` `height[])``{``    ``int` `mark[N + 1];``    ``memset``(mark, 0, ``sizeof` `mark);` `    ``int` `maxLevel = 0;``    ``for` `(``int` `i = 1; i <= N; i++) {` `        ``// count number of nodes``        ``// in every level``        ``if` `(vis[i])``            ``mark[height[i]]++;` `        ``// find the maximum height of tree``        ``maxLevel = max(height[i], maxLevel);``    ``}` `    ``// print odd number of nodes``    ``cout << ``"The levels with odd number of nodes are: "``;``    ``for` `(``int` `i = 1; i <= maxLevel; i++) {``        ``if` `(mark[i] % 2)``            ``cout << i << ``" "``;``    ``}` `    ``// print even number of nodes``    ``cout << ``"\nThe levels with even number of nodes are: "``;``    ``for` `(``int` `i = 1; i <= maxLevel; i++) {``        ``if` `(mark[i] % 2 == 0)``            ``cout << i << ``" "``;``    ``}``}` `// Driver Code``int` `main()``{``    ``// Construct the tree` `    ``/*   1``       ``/   \``      ``2     3``     ``/ \     \``    ``4    5    6``        ``/ \  /``       ``7   8 9  */` `    ``const` `int` `N = 9;` `    ``vector<``int``> tree[N + 1];` `    ``insertEdges(1, 2, tree);``    ``insertEdges(1, 3, tree);``    ``insertEdges(2, 4, tree);``    ``insertEdges(2, 5, tree);``    ``insertEdges(5, 7, tree);``    ``insertEdges(5, 8, tree);``    ``insertEdges(3, 6, tree);``    ``insertEdges(6, 9, tree);` `    ``int` `height[N + 1];``    ``int` `vis[N + 1] = { 0 };` `    ``height = 0;` `    ``// call the dfs function``    ``dfs(1, 0, height, vis, tree);` `    ``// Function to print``    ``printLevelsOddEven(N, vis, height);` `    ``return` `0;``}`

## Java

 `// Java program to print all levels``// with odd and even number of nodes``import` `java.util.*;` `@SuppressWarnings``(``"unchecked"``)``class` `GFG{`` ` `// Function for DFS in a tree``static` `void` `dfs(``int` `node, ``int` `parent,``                ``int` `[]height, ``int` `[]vis,``                ``ArrayList []tree)``{``    ` `    ``// Calculate the level of every node``    ``height[node] = ``1` `+ height[parent];``  ` `    ``// Mark every node as visited``    ``vis[node] = ``1``;``  ` `    ``// Iterate in the subtree``    ``for``(``int` `it : (ArrayList)tree[node])``    ``{``        ` `        ``// If the node is not visited``        ``if` `(vis[it] == ``0``)``        ``{``            ` `            ``// Call the dfs function``            ``dfs(it, node, height, vis, tree);``        ``}``    ``}``}``  ` `// Function to insert edges``static` `void` `insertEdges(``int` `x, ``int` `y,``                        ``ArrayList []tree)``{``    ``tree[x].add(y);``    ``tree[y].add(x);``}``  ` `// Function to print all levels``static` `void` `printLevelsOddEven(``int` `N, ``int` `[]vis,``                               ``int` `[]height)``{``    ``int` `[]mark = ``new` `int``[N + ``1``];``    ``Arrays.fill(mark, ``0``);``    ``int` `maxLevel = ``0``;``    ` `    ``for``(``int` `i = ``1``; i <= N; i++)``    ``{``        ` `        ``// Count number of nodes``        ``// in every level``        ``if` `(vis[i] != ``0``)``            ``mark[height[i]]++;``  ` `        ``// Find the maximum height of tree``        ``maxLevel = Math.max(height[i], maxLevel);``    ``}``  ` `    ``// Print odd number of nodes``    ``System.out.print(``"The levels with odd "` `+``                     ``"number of nodes are: "``);``     ` `    ``for``(``int` `i = ``1``; i <= maxLevel; i++)``    ``{``        ``if` `(mark[i] % ``2` `!= ``0``)``        ``{``            ``System.out.print(i + ``" "``);``        ``}``    ``}``  ` `    ``// Print even number of nodes``    ``System.out.print(``"\nThe levels with even "` `+``                     ``"number of nodes are: "``);``     ` `    ``for``(``int` `i = ``1``; i <= maxLevel; i++)``    ``{``        ``if` `(mark[i] % ``2` `== ``0``)``        ``{``            ``System.out.print(i + ``" "``);``        ``}``    ``}``}``     ` `// Driver code ``public` `static` `void` `main(String []s)``{``    ` `    ``// Construct the tree``     ` `    ``/*   1``       ``/   \``      ``2     3``     ``/ \     \``    ``4    5    6``        ``/ \  /``       ``7   8 9  */``     ` `    ``int` `N = ``9``;``     ` `    ``ArrayList []tree = ``new` `ArrayList[N + ``1``];``     ` `    ``for``(``int` `i = ``0``; i < N + ``1``; i++)``    ``{``        ``tree[i] = ``new` `ArrayList();``    ``}``     ` `    ``insertEdges(``1``, ``2``, tree);``    ``insertEdges(``1``, ``3``, tree);``    ``insertEdges(``2``, ``4``, tree);``    ``insertEdges(``2``, ``5``, tree);``    ``insertEdges(``5``, ``7``, tree);``    ``insertEdges(``5``, ``8``, tree);``    ``insertEdges(``3``, ``6``, tree);``    ``insertEdges(``6``, ``9``, tree);``     ` `    ``int` `[]height = ``new` `int``[N + ``1``];``    ``int` `[]vis = ``new` `int``[N + ``1``];``    ``Arrays.fill(vis, ``0``);``     ` `    ``height[``0``] = ``0``;``     ` `    ``// Call the dfs function``    ``dfs(``1``, ``0``, height, vis, tree);``     ` `    ``// Function to print``    ``printLevelsOddEven(N, vis, height);``}``}` `// This code is contributed by pratham76`

## Python3

 `# Python3 program to print all levels``# with odd and even number of nodes` `# Function for DFS in a tree``def` `dfs(node, parent, height, vis, tree):` `    ``# calculate the level of every node``    ``height[node] ``=` `1` `+` `height[parent]` `    ``# mark every node as visited``    ``vis[node] ``=` `1` `    ``# iterate in the subtree``    ``for` `it ``in` `tree[node]:` `        ``# if the node is not visited``        ``if` `not` `vis[it]:` `            ``# call the dfs function``            ``dfs(it, node, height, vis, tree)``        ` `# Function to insert edges``def` `insertEdges(x, y, tree):` `    ``tree[x].append(y)``    ``tree[y].append(x)` `# Function to print all levels``def` `printLevelsOddEven(N, vis, height):` `    ``mark ``=` `[``0``] ``*` `(N ``+` `1``)``    ` `    ``maxLevel ``=` `0``    ``for` `i ``in` `range``(``1``, N ``+` `1``):` `        ``# count number of nodes in every level``        ``if` `vis[i]:``            ``mark[height[i]] ``+``=` `1` `        ``# find the maximum height of tree``        ``maxLevel ``=` `max``(height[i], maxLevel)``    ` `    ``# print odd number of nodes``    ``print``(``"The levels with odd number"``,``          ``"of nodes are: "``, end ``=` `"")``    ``for` `i ``in` `range``(``1``, maxLevel ``+` `1``):``        ``if` `mark[i] ``%` `2``:``            ``print``(i, end ``=` `" "``)``    ` `    ``# print even number of nodes``    ``print``(``"\nThe levels with even number"``,``          ``"of nodes are: "``, end ``=` `"")``    ``for` `i ``in` `range``(``1``, maxLevel ``+` `1``):``        ``if` `mark[i] ``%` `2` `=``=` `0``:``            ``print``(i, end ``=` `" "``)` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:` `    ``# Construct the tree``    ``N ``=` `9``    ``tree ``=` `[[] ``for` `i ``in` `range``(N ``+` `1``)]` `    ``insertEdges(``1``, ``2``, tree)``    ``insertEdges(``1``, ``3``, tree)``    ``insertEdges(``2``, ``4``, tree)``    ``insertEdges(``2``, ``5``, tree)``    ``insertEdges(``5``, ``7``, tree)``    ``insertEdges(``5``, ``8``, tree)``    ``insertEdges(``3``, ``6``, tree)``    ``insertEdges(``6``, ``9``, tree)` `    ``height ``=` `[``0``] ``*` `(N ``+` `1``)``    ``vis ``=` `[``0``] ``*` `(N ``+` `1``)` `    ``# call the dfs function``    ``dfs(``1``, ``0``, height, vis, tree)` `    ``# Function to print``    ``printLevelsOddEven(N, vis, height)` `# This code is contributed by Rituraj Jain`

## C#

 `// C# program to print all levels``// with odd and even number of nodes``using` `System;``using` `System.Collections;` `class` `GFG{` `// Function for DFS in a tree``static` `void` `dfs(``int` `node, ``int` `parent,``                ``int` `[]height, ``int` `[]vis,``                ``ArrayList []tree)``{``    ` `    ``// Calculate the level of every node``    ``height[node] = 1 + height[parent];`` ` `    ``// Mark every node as visited``    ``vis[node] = 1;`` ` `    ``// Iterate in the subtree``    ``foreach` `(``int` `it ``in` `tree[node])``    ``{``        ` `        ``// If the node is not visited``        ``if` `(vis[it] == 0)``        ``{``            ` `            ``// Call the dfs function``            ``dfs(it, node, height, vis, tree);``        ``}``    ``}``}`` ` `// Function to insert edges``static` `void` `insertEdges(``int` `x, ``int` `y,``                        ``ArrayList []tree)``{``    ``tree[x].Add(y);``    ``tree[y].Add(x);``}`` ` `// Function to print all levels``static` `void` `printLevelsOddEven(``int` `N, ``int` `[]vis,``                               ``int` `[]height)``{``    ``int` `[]mark = ``new` `int``[N + 1];``    ``Array.Fill(mark, 0);`` ` `    ``int` `maxLevel = 0;``    ``for``(``int` `i = 1; i <= N; i++)``    ``{``        ` `        ``// Count number of nodes``        ``// in every level``        ``if` `(vis[i] != 0)``            ``mark[height[i]]++;`` ` `        ``// Find the maximum height of tree``        ``maxLevel = Math.Max(height[i], maxLevel);``    ``}`` ` `    ``// Print odd number of nodes``    ``Console.Write(``"The levels with odd "` `+``                  ``"number of nodes are: "``);``    ` `    ``for``(``int` `i = 1; i <= maxLevel; i++)``    ``{``        ``if` `(mark[i] % 2 != 0)``        ``{``            ``Console.Write(i + ``" "``);``        ``}``    ``}`` ` `    ``// Print even number of nodes``    ``Console.Write(``"\nThe levels with even "` `+``                  ``"number of nodes are: "``);``    ` `    ``for``(``int` `i = 1; i <= maxLevel; i++)``    ``{``        ``if` `(mark[i] % 2 == 0)``        ``{``            ``Console.Write(i + ``" "``);``        ``}``    ``}``}``    ` `// Driver code ``static` `void` `Main()``{``      ` `    ``// Construct the tree``    ` `    ``/*   1``       ``/   \``      ``2     3``     ``/ \     \``    ``4    5    6``        ``/ \  /``       ``7   8 9  */``    ` `    ``int` `N = 9;``    ` `    ``ArrayList []tree = ``new` `ArrayList[N + 1];``    ` `    ``for``(``int` `i = 0; i < N + 1; i++)``    ``{``        ``tree[i] = ``new` `ArrayList();``    ``}``    ` `    ``insertEdges(1, 2, tree);``    ``insertEdges(1, 3, tree);``    ``insertEdges(2, 4, tree);``    ``insertEdges(2, 5, tree);``    ``insertEdges(5, 7, tree);``    ``insertEdges(5, 8, tree);``    ``insertEdges(3, 6, tree);``    ``insertEdges(6, 9, tree);``    ` `    ``int` `[]height = ``new` `int``[N + 1];``    ``int` `[]vis = ``new` `int``[N + 1];``    ``Array.Fill(vis, 0);``    ` `    ``height = 0;``    ` `    ``// Call the dfs function``    ``dfs(1, 0, height, vis, tree);``    ` `    ``// Function to print``    ``printLevelsOddEven(N, vis, height);``}``}` `// This code is contributed by rutvik_56`

## Javascript

 ``
Output:
```The levels with odd number of nodes are: 1 3 4
The levels with even number of nodes are: 2```

Time Complexity: O(N)
Auxiliary Space: O(N)

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