Construct a Binary Tree from given Inorder and Level Order Traversal
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Algorithms and Data Structures: TheAlgorist.com
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Problem Statement:
Given an inorder and level order traversal, construct a binary tree from that.
Solution:
Let's take the below example:
Given input array inorder[] = { 4, 2, 5, 1, 6, 3, 7 }
Given input array levelOrder[] = { 1, 2, 3, 4, 5, 6, 7 }
- First element in the levelorder [] will be the root of the tree, here it is 1.
- Now the search element 1 in inorder[], say you find it at position i, once you find it, make note of elements which are left to i (this will construct the leftsubtree) and elements which are right to i ( this will construct the rightSubtree).
- Suppose in previous step, there are X number of elements which are left of ‘i’ (which will construct the leftsubtree), but these X elements will not be in the consecutive in levelorder[] so we will extract these elements from levelorder[] by maintaining their sequence and store it in an array say newLeftLevel[].
- Similarly if there are Y number of elements which are right of ‘i’ (which will construct the rightsubtree), but these Y elements will not be in the consecutive in levelorder[] so we will extract these elements from levelorder[] by maintaining their sequence and store it in an array say newRightLevel[].
- From previous two steps construct the left and right subtree and link it to root.left and root.right respectively by making recursive calls using newLeftLevel[] and newRightLevel[].
See the picture for better explanation.
Java code:
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