843. Sum of All Nodes

Given the root of a binary tree, return the sum of all node values. The tree is given as a level-order array with null for missing children.

Input: A level-order array of the tree.

Output: Integer — the sum of all values.

Examples

Example 1

Input: [1,2,3,4,5,null,6]
Output: 21
Explanation: 1+2+3+4+5+6 = 21.

Example 2

Input: [1]
Output: 1
Explanation: Single node.

Example 3

Input: []
Output: 0
Explanation: Empty tree.