Kth largest sum in a binary tree
May 21, 2023heap tree
Problem URL: Kth largest sum in a binary tree
We will traverse the whole tree with BFS and store each levels sum in a list. Then, we will use a heap to get the
k-th largest sum. We will also check if the tree doesn't have enough levels to reach k, then we return -1.
# 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 kthLargestLevelSum(self, root: Optional[TreeNode], k: int) -> int: levels =  q = collections.deque([root]) while q: qLen, levelSum = len(q), 0 for _ in range(qLen): node = q.popleft() levelSum += node.val if node.left: q.append(node.left) if node.right: q.append(node.right) levels.append(levelSum) if len(levels) < k: return -1 return heapq.nlargest(k, levels)[-1]
O(nlog(k)) where n is the number of nodes in the tree.
O(n) where n is the number of nodes in the tree.