DSA - 2 new (DFS Pattern, Recursion to DP Insight)

572. Subtree of Another Tree

Insight — DFS (preorder) serialization: if subRoot traversal string is a substring of root traversal string, then it is a subtree (ensure null markers like “N” + delimiters for exact match).

Comment - Could solve. Core idea understood, but implementation still not smooth. Edge cases and clean serialization need more practice.

62. Unique Paths

Insight — brute force = DFS on grid (only right & down), total paths = paths(right) + paths(down); then optimise using DP (memoization / tabulation)

Comment - Could not solve. Hesitated to explore full recursion tree. Pattern was known but not applied. Need to reinforce habit: recursion → memoization → tabulation (Aditya Verma DP approach).