How do you solve Deepest Leaves Sum on LeetCode?

Deepest Leaves Sum (LeetCode #1302) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Using BFS allows us to efficiently calculate the sum of the deepest leaves in one pass.

What is the brute force solution for Deepest Leaves Sum?

The brute force approach for Deepest Leaves Sum is Brute Force, with O(n²) time complexity and O(1) space complexity. In this approach, we will first find the maximum depth of the tree and then traverse the tree again to sum the values of the leaves at that depth. This is straightforward but inefficient. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Deepest Leaves Sum?

Deepest Leaves Sum uses the following concepts: Tree, Depth-First Search, Breadth-First Search, Binary Tree. The recommended patterns to study are: Breadth-First Search (BFS), Depth-First Search (DFS).

What are the interview tips for Deepest Leaves Sum?

Always clarify the problem requirements and constraints before diving into coding. Think about the efficiency of your solution and whether you can reduce the number of traversals. Practice explaining your thought process as you code; this helps interviewers understand your approach.

What are common mistakes when solving Deepest Leaves Sum?

Not considering edge cases like an empty tree. Confusing depth with level; depth is the distance from the root, while level is the number of nodes at that depth.

#1302

Deepest Leaves Sum

Medium

TreeDepth-First SearchBreadth-First SearchBinary TreeBreadth-First Search (BFS)Depth-First Search (DFS)

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

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Intuition

Time O(n)Space O(n)

This approach uses a single traversal of the tree to simultaneously calculate the maximum depth and the sum of the deepest leaves. This is efficient and avoids redundant work.

⚙️

Algorithm

3 steps

1Step 1: Use a queue for level order traversal (BFS) to explore each level of the tree.
2Step 2: For each level, sum the values of the nodes.
3Step 3: Continue until all levels are processed, returning the sum of the last level.

solution.py17 lines

1from collections import deque
2
3def deepestLeavesSum(root):
4    if not root:
5        return 0
6    queue = deque([root])
7    while queue:
8        level_sum = 0
9        level_size = len(queue)
10        for _ in range(level_size):
11            node = queue.popleft()
12            level_sum += node.val
13            if node.left:
14                queue.append(node.left)
15            if node.right:
16                queue.append(node.right)
17    return level_sum

ℹ

Complexity note: This complexity is due to the single traversal of the tree (O(n)) and the space used by the queue, which can hold up to O(n) nodes in the worst case.

1Using BFS allows us to efficiently calculate the sum of the deepest leaves in one pass.
2The maximum depth can be determined while summing the values, avoiding redundant traversals.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.