Add DP and Binary tree questions

README.md

@@ -300,7 +300,8 @@ Collection of interesting questions and solutions that involve data structures,
   4.9 [Serialize and Deserialize a Binary tree](https://github.com/harishvc/challenges/blob/master/binary-tree-construct.py) :boom: :thumbsup: :rocket:  
   4.10 [Given preorder and inorder traversal construct postorder traversal](https://github.com/harishvc/challenges/blob/master/binary-tree-preorder-to-postorder.py) :boom: :thumbsup:  
   4.11 Given a linked list, construct a balanced tree with the same in-order traversal
-  4.12 Find the longest branch  
+  4.12 Find the longest branch
+  4.13 [Invert a Binary Tree](https://github.com/harishvc/challenges/blob/master/binary-tree-invert.py) :bulb: [TODO]   
 
 ### Binary Search Tree (BST)  
 1.  Create BST  
@@ -378,11 +379,15 @@ Collection of interesting questions and solutions that involve data structures,
     5.1 [Find all possible combinations to reach a total] (https://github.com/harishvc/challenges/blob/master/coin-change.py) :bulb: :boom:    
     5.2 [Find all possible combinations to reach a total using lookup] (https://github.com/harishvc/challenges/blob/master/coin-change-with-lookup.py) :bulb: :boom:  
     5.3. [Minimum # coins needs to reach the total](https://github.com/harishvc/challenges/blob/master/dp-minimum-coins.py)  :rocket: :notes:     
-6. [Find #steps to convert string1 to string 2 using operations insert,remove,replace](https://github.com/harishvc/challenges/blob/master/dp-string-distance.py)  :thumbsup:  :rocket:
-7. [How many different 10-digit numbers can be formed starting from 1? movement from 1 digit to the next is similar to the movement of the Knight in a chess game] (https://github.com/harishvc/challenges/blob/master/dp-knight-chess-movement.py) :bulb: :rocket:  
-8. Given two sequences find the longest palindrome
-9. [Implement Unix diff command](https://github.com/harishvc/challenges/blob/master/unix-diff.py)
-10. [Given stock prices during a time period find the maximum gain that can be made from one purchase followed by one sale of the stock](https://github.com/harishvc/challenges/blob/master/find-maximum-gain.py) :memo:
+6. Input string and dictionary of words     
+   6.1 Can the input word be split using space-separated sequence of dictionary words?    
+   6.2 Split the input string into a space-separated sequence of dictionary words if possible  
+   6.3 Find all possible space-separated sequence of dictionary words   
+7. [Find #steps to convert string1 to string 2 using operations insert,remove,replace](https://github.com/harishvc/challenges/blob/master/dp-string-distance.py)  :thumbsup:  :rocket:
+8. [How many different 10-digit numbers can be formed starting from 1? movement from 1 digit to the next is similar to the movement of the Knight in a chess game] (https://github.com/harishvc/challenges/blob/master/dp-knight-chess-movement.py) :bulb: :rocket:  
+9. Given two sequences find the longest palindrome
+10. [Implement Unix diff command](https://github.com/harishvc/challenges/blob/master/unix-diff.py)
+11. [Given stock prices during a time period find the maximum gain that can be made from one purchase followed by one sale of the stock](https://github.com/harishvc/challenges/blob/master/find-maximum-gain.py) :memo:
 
 ### Design & Algorithms
 1.  [Given a million points (x, y), give an O(n) solution to find the n points closest to (0, 0)](https://github.com/harishvc/challenges/blob/master/nearest-point.py)

binary-tree-invert.py

@@ -0,0 +1,2 @@
+#Invert a Binary Tree
+#https://www.quora.com/Is-invert-a-binary-tree-a-good-question-for-Google-to-ask-in-a-technical-interview