Find the diagonal sum of given binary tree

Given a binary tree, calculate sum of all nodes for each diagonal having negative slope (\). Assume that the left and right child of a node makes 45 degree angle with the parent.

 

For example, consider below binary tree having three diagonals (marked in red). The sum of diagonals is 10, 15 and 11.

diagonal-sum

 


 

This problem can be easily solved with the help of Hashing. The idea is to create an empty map where each key in the map represents a diagonal in the binary tree and its value maintains sum of all nodes present in the diagonal. Then we do a pre-order traversal of the tree and update the map. For each node, we recurse for its left subtree by increasing diagonal by 1 and recurse for right subtree with same diagonal.

 
C++ implementation –
 

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The time complexity of above solution is O(n) and auxiliary space used by the program is O(n).
 

Exercise:
1. Extend the solution to print nodes of every diagonal.
2. Modify the solution to print diagonal sum for diagonals having positive slope (/).
 

Thanks for reading.




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