LC-0968 Hard LeetCode

968. Binary Tree Cameras

Dynamic Programming Tree Depth-First Search Binary Tree

Read the full problem statement on LeetCode.

Difficulty: hard Acceptance: 47% Topics: Dynamic Programming, Tree, Depth-First Search, Binary Tree

Reading material

1-D Dynamic Programming 16 min Trees & Traversals 18 min

Reference solution (spoiler · python)

# Time:  O(n)
# Space: O(h)

# Definition for a binary tree node.
class TreeNode(object):
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


class Solution(object):
    def minCameraCover(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        UNCOVERED, COVERED, CAMERA = range(3)
        def dfs(root, result):
            left = dfs(root.left, result) if root.left else COVERED
            right = dfs(root.right, result) if root.right else COVERED
            if left == UNCOVERED or right == UNCOVERED:
                result[0] += 1
                return CAMERA
            if left == CAMERA or right == CAMERA:
                return COVERED
            return UNCOVERED
        
        result = [0]
        if dfs(root, result) == UNCOVERED:
            result[0] += 1
        return result[0]

Solution from kamyu104/LeetCode-Solutions · MIT