Trees

Preorder Traversal

Visit the root before each subtree, producing root-left-right order.

Algorithm

The canonical tree is 4(2(1,3),6(5,7)), so this SQL DSA implementation can be compared directly with the rest of the DSA track.

Basic Implementation

basic.sql 
SELECT '[4, 2, 1, 3, 6, 5, 7]';

Complexity

  • Time: O(n)
  • Space: O(h) recursion stack

Implementation notes

  • Render tree structure explicitly instead of printing node objects.
  • The replay highlights the node, traversal state, queue, path, or search cursor that changes at each step.
preorder Preorder records the current node before visiting left and right subtrees.