Given the root of a binary tree, the level of its root is 1, the level of its children is 2, and so on. Return the smallest level x such that the sum of all the values of nodes at level x is maximal. Example 1: Input: root = [1,7,0,7,-8,null,null] Output: 2 Explanation: Level 1 sum = 1. Level 2 sum = 7 + 0 = 7. Level 3 sum = 7 + -8 = -1. So we return the level with the maximum sum which is level 2. Example 2: Input: root = [989,null,10250,98693,-89388,null,null,null,-32127] Output: 2 Constraints: The number of nodes in the tree is in the range [1, 104]. -105 <= Node.val <= 105