Floor register: Total receipt
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Inputs
root is the top node of a binary tree. Examples list nodes one level at a time, from left to right. null marks a missing child; [] means no tree. Each node stores its number in val. Its left and right links point to children. The runner builds the nodes for you.
Your tasks
- Create a list
levelSums.rootis the top node of a binary tree. Each node has a value and up to two children. Therootis at depth 0, its children are at depth 1, and so on. Add the values at each depth. Put one sum per depth inlevelSums, starting at depth 0. Missing children add nothing. An empty tree gives an emptylevelSums. - Add up every number in
levelSums. Store the sum intotal. - Complete
floorRegisterTotalReceiptso it returnstotal. Return it, do not print it.
Example
If root is [2, null, 9, -5, 2], then levelSums is [2, 9, -3] and floorRegisterTotalReceipt returns 8.
Rules
- If
levelSumsis empty,totalis 0.
Test data
TEST DATA 1: root is [3, null, -3, 0, 3].
TEST DATA 2: root is [4, null, 4, 4, -5].
Examples
Input: root = [3,null,-3,0,3] Output: 3
levelSums is [3, -3, 3]. Add its numbers to get 3. Return 3.
Input: root = [4,null,4,4,-5] Output: 7
levelSums is [4, 4, -1]. Add its numbers to get 7. Return 7.
Input: root = [] Output: 0
levelSums is []. Add its numbers to get 0. Return 0.
Input limits
- 0 <= node count <= 31; null marks a missing child and does not count as a node.
- Answers fit in a signed 32-bit integer: -2,147,483,648 through 2,147,483,647.
- Input numbers have no decimal part. They range from -1,000,000 to 1,000,000. Follow any extra input rules in task 1.
- Linked lists do not loop back to an earlier node. Tree examples list nodes by level; null means a missing child. The runner builds the nodes shown in the examples.
Efficiency goal
Big-O describes how the work or memory needed grows as the input gets larger.
Efficiency goal: time O(n); extra memory, including the helper list, O(n). n is the number of nodes. These labels describe how work and memory grow with the input.
Practice focus
Build levelSums first, then return exactly what the tasks ask for. Follow the order, keep repeated values when the rule says so, and check the empty case.