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Level Order Traversal, Print each level in separate line.
Objective: Given a Binary tree , Print each level of a tree in separate line.
NOTE : This problem is very similar " Create Linked Lists of all the nodes at each depth "
Input: A binary tree
Output: Each level of binary tree, in one line
Example:
Approach:
Naive Approach:
- Get the height of the tree.
- Put a for loop for each level in tree.
- for each level in step 2, do pre order traversal and print only when height matches to the level.
- Look at the code for better explanation
Time Complexity : O(N^2) - because each level you are traversing the entire tree.
Better Solution : Time Complexity - O(N)
- Do the level order traversal using queue(Breadth First Search). Click here to know about how to level order traversal.
- For getting all the nodes at each level, before you take out a node from queue, store the size of the queue in a variable, say you call it as levelNodes.
- Now while levelNodes>0, take out the nodes and print it and add their children into the queue.
- After this while loop put a line break.
while(!q.isEmpty()){ levelNodes = q.size(); while(levelNodes>0){ Node n = (Node)q.remove(); System.out.print(" " + n.data); if(n.left!=null) q.add(n.left); if(n.right!=null) q.add(n.right); levelNodes--; } System.out.println(""); }
- Since we had taken the queue size before we add new nodes, we will get the count at each level and after printing this count, put a line break, see the example below
Output by Naive Approach : 5 10 15 20 25 30 35 Output by Better Approach : 5 10 15 20 25 30 35
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