Construct Binary Tree from Preorder and Postorder Traversal | Leetcode 889 | codestorywithMIK
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Hi Everyone, this is the 57th video of our Playlist "Binary Tree : Popular Interview Problems".
Now we will be solving a good Binary Tree problem - Construct Binary Tree from Preorder and Postorder Traversal | Brute Force | Optimised | Leetcode 889 | codestorywithMIK
Problem Name : Construct Binary Tree from Preorder and Postorder Traversal | Brute Force | Optimised | Leetcode 889 | codestorywithMIK
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My solutions on Github(C++ & JAVA) - https://github.com/MAZHARMIK/Interview_DS_Algo/blob/master/Tree/Construct Binary Tree from Preorder and Postorder Traversal.cpp
Leetcode Link : https://leetcode.com/problems/construct-binary-tree-from-preorder-and-postorder-traversal
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Video Summary :
Approach 1 (Brute Force)
This approach recursively reconstructs the binary tree by identifying the root from the preorder array. It then finds the left subtree's root in the postorder array by iterating through it. The left and right subtrees are built using the identified segments of the preorder and postorder arrays. This results in an O(n^2) time complexity due to repeated searches in the postorder array.
Approach 2 (Using Map for Optimization)
This approach improves efficiency by using a hashmap to store indices of postorder values. Instead of iterating through the postorder array, it directly finds the left subtree’s root index in O(1) time. This significantly reduces redundant searches, making the algorithm run in O(n) time. The recursive structure remains the same, but the use of a hashmap optimizes subtree identification.
✨ Timelines✨
00:00 - Introduction
0:16 - Motivation
00:43 - Problem Explanation
2:57 - Similar Problems
3:21 - Thought Process Approach-1
22:17 - Story To Code
30:25 - Time & Space Complexity
31:18 - Coding Approach-1
35:59 - Optimisation Approach-2
38:01 - Coding Approach-2
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