solved using recursion, base case is it has a left leaf, sum it if not call it on left subtree, if right subtree exists call it on right subtree and sum it.
solved using recursion, base case is it has a left leaf, sum it if not call it on left subtree, if right subtree exists call it on right subtree and sum it.

young-geng/leet_code,young-geng/leet_code