The Runtime Theory
mediumLeetCode#dfs#path-state

Count Good Nodes in Binary Tree

Count nodes whose value is at least every value on the path from the root to that node.

The Runtime Theory Team25 min read
Solve it

Solving happens on the judge — come back and mark it done

Sample cases

inroot=[3,1,4,3,null,1,5]

out4

inroot=[3,3,null,4,2]

out3

inroot=[1]

out1

Count nodes whose value is at least every value on the path from the root to that node.

A good solution should

  • State the invariant or decision rule that makes the approach correct.
  • Explain the time and space complexity in terms of the input sizes and required output.
  • Handle empty, minimal, duplicate, and boundary-shaped inputs covered by the contract.

Reasoning prompt

Carry the maximum seen so far into each child. Clarify that equality counts as good.

Use the linked judge for the canonical problem. The examples above are compact TRT checks; write additional cases before submitting, especially for the boundary that tends to break your chosen invariant.

More practice in this topic

easy · treesBalanced Binary Treemedium · treesBinary Tree Level Order Traversalmedium · treesBinary Tree Right Side View

One dispatch a week

The trace behind each problem, the tradeoff that explains it, and one technical dispatch per week — no noise.

One technical dispatch per week. No noise.

Not started

Sign in to save your learning progress.

Sign in to save