Leetcode Problem 1530. Number of Good Leaf Nodes Pairs

1530. Number of Good Leaf Nodes Pairs

Leetcode Solutions

Postorder Traversal with Distance Tracking

  1. Define a recursive function dfs that takes a TreeNode and returns a list of distances of all leaf nodes to that node.
  2. If the current node is null, return an empty list.
  3. If the current node is a leaf node, return a list containing only 1 (distance from the leaf to itself).
  4. Recursively call dfs on the left and right children of the current node to get the list of distances from the left and right subtrees.
  5. For each pair of distances from the left and right lists, if their sum is less than or equal to distance, increment a global count variable.
  6. Create a new list to hold the incremented distances for the current node's parent.
  7. Increment each distance from the left and right lists by 1 and add them to the new list.
  8. Return the new list of incremented distances.
  9. Call dfs on the root node and return the global count variable.
UML Thumbnail

DFS with Parent Tracking

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