Standard Bar Binary Trees · Medium Problems O(n) · O(h)
A stage-rigging contractor hangs lighting trusses from a binary tree of support arms. Insurance rules say the structure is certified only if, at every junction, the two hanging chains differ in length by at most one unit — otherwise torque builds up dangerously. The auditor needs a single pass that certifies or condemns the whole rig before the show is booked.
Input: The root of a binary tree given as a level-order array where null marks a missing child. An empty array is a valid (empty) tree.
Output: Return true if the tree is height-balanced at every node, false otherwise.
0 <= number of nodes <= 10^5-100 <= node value <= 100Input: {"tree":[3,9,20,null,null,15,7]}
Output: true
Every junction's two chains differ by at most one unit.
Input: {"tree":[1,2,2,3,3,null,null,4,4]}
Output: false
At the root, the left chain runs 3 deep but the right chain only 1 — a gap of 2.