[Approach] Check if a Binary Tree is a Binary Search Tree (BST)

Problem

Given a binary tree, find out if it is a binary search tree or not.

 

Approach 1

  • You can traverse the tree in in-order way, and see if the elements are assending.

    • You may either put the elements into an array and see if the array is sorted in assending way,

    • or while traversing see if the current element is always greater than or equal to previous element.

      • return false is current data is less than previously printed data.

      • may use a static variable to hold the last printed value.

  • Complete solution can be found @ http://javajee.com/solution-checking-if-a-binary-tree-is-a-binary-search....

 

Approach 2

  • For a BST, all left nodes should be less than or equal to current node and current node must be less than all right nodes.

  • We will have a recursive function that checks if this property is true for root node and all its sub trees:

    • If the method get null node, it may return true, and should be first checked (exit condition for the recursion).

    • Check if all left nodes are less than or equal to current node and current node is less than all right nodes

      • Pass current minimum and current data to left subtree

      • Pass current data and current max to right sub trees

  • Complete solution can be found @ http://javajee.com/solution-check-if-a-binary-tree-is-a-binary-search-tr....

 

Note:

  • Here, I will giving some of the common approach(es) for the problems on trees and graph given earlier.

  • The solutions may not be the best. But it will surely give enough information to start thinking. Convert them into algorithms (or code) to gain best out of these.

  • Original list of questions can be found @ http://javajee.com/problems-list-of-problems-on-trees-and-graphs-for-int....

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