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Classic problem #965EasyTreeDepth-First SearchBreadth-First SearchBinary Tree

Univalued Binary Tree

Real-world version: Single Channel Relay Network
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The statement here is our own: the same inputs, outputs and technique.

A broadcast operator runs a relay network shaped as a binary tree. One relay sits at the head of the network, and every relay feeds up to two relays below it, a first branch and a second branch, either of which may be empty. Each relay is tuned to a channel, written as a number.

The network arrives as channels, a level-order listing. The first entry is the channel of the relay at the head. After that, the listing gives the first branch then the second branch of each relay already listed, in the order those relays appear, writing null wherever a branch is empty. Slots below a null are never written down, and the trailing run of null entries is left off.

The network is easiest to maintain when it runs on one channel throughout. Return true when every relay in the network is tuned to the same channel, and false otherwise.

Examples

Example 1

Input
channels = [6, 6, 6, null, 6]
Output
true

The listing names four relays and every one of them sits on channel 6. The `null` is the empty first branch below the relay listed second, not a relay.

Example 2

Input
channels = [3, 3, null, 3, null, 3, null, 9]
Output
false

Each relay here feeds exactly one relay below it, giving a chain of channels 3, 3, 3, 3 and 9. The relay at the far end of the chain is on channel 9, which is not the channel at the head.

Example 3

Input
channels = [8]
Output
true

The network is a single relay on channel 8, and it agrees with itself.

Constraints

  • The number of relays in the network is in the range [1, 100].
  • 1 <= channels.length <= 200
  • 0 <= channels[i] <= 99
  • An entry of channels that is null marks an empty branch rather than a relay.
  • channels[0] is never null.

The signature

The editor starts with this. It matches the parent problem's shape, so a solution that works here works on a standard judge unchanged.

Python
def is_single_channel(channels: list[int | None]) -> bool:
Java
public boolean isSingleChannel(Integer[] channels)

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