Introduction
This is going to be a short post. The problem statement at hand is to write PostOrder Node Iterator of Binary Tree. For those who do not know the Iterator Design Pattern or Post Order Successor, check the next section.
Iterator Design Pattern
This pattern is used to iterate through a collection or group. The Java Iterator supports the following three methods :
hasNext() : returns a boolean true if the collection has elements after the last returned element, false otherwise.
next() : returns the next element in the collection.
remove() : removes the element from the coll...

Read More
# Interview Questions

This category contains few tricky questions asked in interviews..

## Find if a Tree is Subtree of another Tree

Introduction
This is a simple yet non trivial problem. Given two trees we need to evaluate if one tree is the sub tree of the other. If the condition is satisfied, it returns true, else it returns false.
The definition of sub tree must not be ambiguous. We say that two trees are equal if they are structurally equal and their corresponding nodes have equal keys.
Equality of trees
Remember that subtree and contains relation are not the same. It may be possible that a tree T1 contains another tree T2 and still T2 is not a sub tree of T1.
This also means that all subtree satisfies the con...

Read More
## Minimum Range over K arrays

Introduction
This is one interesting problem with a non-trivial solution, this has been asked in couple of good interviews. Here goes the problem statement.
"Given K positive integer arrays, each of which contains elements in sorted order. Find a range of integers such that it must contain at least one element from each array and the range is minimum."
May be a diagram can make this more clear. Here you go!
Understanding the Minimum Range over K arrays problem.
In the above diagram we have 3 arrays each containing elements in increasing order. Now, let us identify a range which cont...

Read More
## Shortest path in Binary Search Tree

Introduction
Another interview question for the most interesting data structure called BST (Binary Search Tree). To know more about BSTs check my previous post.
Problem Statement : Given a Binary Search Tree, keyed on positive integers. The task is to find the Shortest path in Binary Search Tree which adds up to the number K. If no such path exists, return a message accordingly.
Understanding the problem
A node in a binary search tree always has a higher key at its right child compared to its left child. There are many path running from the roots to the leaves. When we add up the key val...

Read More
## Dynamic Programming – Longest Palindromic Sequence

[nextpage title="Introduction"]
Palindromes are fascinating character sequences in a string. A palindrome is a string which reads the same when read from either of the ends. This post in particular talks about palindromic sub sequences.
To know more about a sub sequence, please check my post on Longest Common Sub sequence.
A palindromic sequence means a sequence of characters which is a palindrome. Now, we must understand it clearly that we are talking about a sub sequence and not a substring.
Understanding the Longest Palindromic Subsequence problem better
It is really easy to say if...

Read More