Problem

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

Note: A leaf is a node with no children.

Example:

Given the below binary tree and sum = 22,

         5
        / \
       4   8
      /   / \
     11  13  4
    /  \      \
   7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

Pre analysis

Simple recurrence pattern should work/