In Python: def sum_tree_values(root): total_sum = root.value # Check if I reached a leaf if root.left is None and root.right is None: return total_sum else: # not a leaf if root.left is not None: # go to left subtree total_sum += sum_tree_values(root.left) if root.right is not None: # go to right subtree total_sum += sum_tree_values(root.right) return total_sum

Do any traversal, and then you can get the answer by adding the value of each node when you reach that node using referenced int passing, or updating a static variable.

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struct node int data; struct node *next; int sum(node* current) if (current == NULL) return 0 return current->data+sum(current->left)+sum(current->right) total = sum(root)