README.md

2385. Amount of Time for Binary Tree to Be Infected

You are given the root of a binary tree with unique values, and an integer start. At minute 0, an infection starts from the node with value start.

Each minute, a node becomes infected if:

• The node is currently uninfected.
• The node is adjacent to an infected node.

Return the number of minutes needed for the entire tree to be infected.

Example 1:

Input: root = [1,5,3,null,4,10,6,9,2], start = 3
Output: 4
Explanation: The following nodes are infected during:
- Minute 0: Node 3
- Minute 1: Nodes 1, 10 and 6
- Minute 2: Node 5
- Minute 3: Node 4
- Minute 4: Nodes 9 and 2
It takes 4 minutes for the whole tree to be infected so we return 4.

Example 2:

Input: root = [1], start = 1
Output: 0
Explanation: At minute 0, the only node in the tree is infected so we return 0.

Constraints:

• The number of nodes in the tree is in the range [1, 105].
• 1 <= Node.val <= 105
• Each node has a unique value.
• A node with a value of start exists in the tree.

Solutions (Python)

1. Solution

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def amountOfTime(self, root: Optional[TreeNode], start: int) -> int:
        def setParent(root: Optional[TreeNode]) -> None:
            if root is None:
                return

            if root.left is not None:
                root.left.parent = root
                setParent(root.left)
            if root.right is not None:
                root.right.parent = root
                setParent(root.right)

        def findNode(root: Optional[TreeNode], val: int) -> Optional[TreeNode]:
            if root is None:
                return
            if root.val == val:
                return root
            findleft = findNode(root.left, val)
            if findleft is not None:
                return findleft
            return findNode(root.right, val)

        setParent(root)
        root.parent = None
        infected = {start}
        deque = collections.deque([(findNode(root, start), 0)])
        ret = 0

        while len(deque) > 0:
            node, minutes = deque.popleft()
            ret = minutes
            if node.parent is not None and node.parent.val not in infected:
                infected.add(node.parent.val)
                deque.append((node.parent, minutes + 1))
            if node.left is not None and node.left.val not in infected:
                infected.add(node.left.val)
                deque.append((node.left, minutes + 1))
            if node.right is not None and node.right.val not in infected:
                infected.add(node.right.val)
                deque.append((node.right, minutes + 1))

        return ret