Count Good Nodes in Binary Tree

Given a binary tree root, a node X in the tree is named good if in the path from root to X there are no nodes with a value greater than X.

Return the number of good nodes in the binary tree.

 

Example 1:

Input: root = [3,1,4,3,null,1,5]
Output: 4
Explanation: Nodes in blue are good.
Root Node (3) is always a good node.
Node 4 -> (3,4) is the maximum value in the path starting from the root.
Node 5 -> (3,4,5) is the maximum value in the path
Node 3 -> (3,1,3) is the maximum value in the path.

Example 2:

Input: root = [3,3,null,4,2]
Output: 3
Explanation: Node 2 -> (3, 3, 2) is not good, because "3" is higher than it.

Example 3:

Input: root = [1]
Output: 1
Explanation: Root is considered as good.

 

Constraints:

  • The number of nodes in the binary tree is in the range [1, 10^5].
  • Each node's value is between [-10^4, 10^4].
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 goodNodes(self, root: TreeNode) -> int:
        paths = [(root, root.val)]
        ctr = 0
        while len(paths) > 0:
            curr, currmax = paths.pop()
            if curr.val >= currmax:
                ctr += 1
            if curr.left:
                paths.append((curr.left, max(currmax, curr.left.val)))
            if curr.right:
                paths.append((curr.right, max(currmax, curr.right.val)))
        return ctr

Comments

Post a Comment

Popular posts from this blog

Encrypt and Decrypt Strings

You are given a character array keys containing unique characters and a string array values containing strings of length 2. You are also given another string array dictionary that contains all permitted original strings after decryption. You should implement a data structure that can encrypt or decrypt a 0-indexed string. A string is encrypted with the following process: For each character c in the string, we find the index i satisfying keys[i] == c in keys . Replace c with values[i] in the string. Note that in case a character of the string is not present in keys , the encryption process cannot be carried out, and an empty string "" is returned. A string is decrypted with the following process: For each substring s of length 2 occurring at an even index in the string, we find an i such that values[i] == s . If there are multiple valid i , we choose any one of them. This means a string could have multiple possible strings it can decrypt t...
Read more

Degree of an Array

Given a non-empty array of non-negative integers nums , the degree of this array is defined as the maximum frequency of any one of its elements. Your task is to find the smallest possible length of a (contiguous) subarray of nums , that has the same degree as nums .   Example 1: Input: nums = [1,2,2,3,1] Output: 2 Explanation: The input array has a degree of 2 because both elements 1 and 2 appear twice. Of the subarrays that have the same degree: [1, 2, 2, 3, 1], [1, 2, 2, 3], [2, 2, 3, 1], [1, 2, 2], [2, 2, 3], [2, 2] The shortest length is 2. So return 2. Example 2: Input: nums = [1,2,2,3,1,4,2] Output: 6 Explanation: The degree is 3 because the element 2 is repeated 3 times. So [2,2,3,1,4,2] is the shortest subarray, therefore returning 6.   Constraints: nums.length will be between 1 and 50,000. nums[i] will be an integer between 0 and 49,999. SOLUTION: from collections import defaultdict class Solution : def findShortestSubArr...
Read more

Minimum Sum of Four Digit Number After Splitting Digits

You are given a positive integer num consisting of exactly four digits. Split num into two new integers new1 and new2 by using the digits found in num . Leading zeros are allowed in new1 and new2 , and all the digits found in num must be used. For example, given num = 2932 , you have the following digits: two 2 's, one 9 and one 3 . Some of the possible pairs [new1, new2] are [22, 93] , [23, 92] , [223, 9] and [2, 329] . Return the minimum possible sum of new1 and new2 .   Example 1: Input: num = 2932 Output: 52 Explanation: Some possible pairs [new1, new2] are [29, 23], [223, 9], etc. The minimum sum can be obtained by the pair [29, 23]: 29 + 23 = 52. Example 2: Input: num = 4009 Output: 13 Explanation: Some possible pairs [new1, new2] are [0, 49], [490, 0], etc. The minimum sum can be obtained by the pair [4, 9]: 4 + 9 = 13.   Constraints: 1000 <= num <= 9999 SOLUTION: class Solution : def minimumSum ( self,...
Read more