interview questions answers continued

Tree Flattening
Question : How do you flatten a binary tree ?
A binary tree can be flattened into an array by storing the left and the right siblings at index positions 2i and 2i+1 as in the case of a heap.
A binary tree can be flattened into a linked list, breadth first by keeping a queue to keep the siblings.
So as you encounter nodes, enqueue it and as you dequeue the nodes, enqueue the siblings. You can have pointers to the next sibling at the same level. Or you can mark the leftmost nodes in the tree in your linked list so that all the siblings breadth wise at the same level in the tree occur between two such marked nodes.
There are some other solutions as well using recursion or storage by keeping track of positions in the tree.

Design a class library to writing game cards.
Game cards is a collection of distinct cards that lend themselves to various groupings and operations.  Use  a collection that works with LINQ like methods

How will you write a find and replace tool  ?
A find and replace tool takes two input strings - one that is used for searching and the other that is used to replace the occurance.  These two are independent operations. When the text is to be deleted, the replacement string is empty. In such cases, rest of the string after the occurance is moved or copied. Search for the next occurance can resume from the current location or all occurances can be found initially.

There is a very large array, in which all the numbers are repeated once except one number. Tell how will you find that number
We can maintain a candidate list and an exclusion list. Numbers that we have seen before are moved to the exclusion list and skipped.