Trees & Binary Trees Interview Questions & Solutions

Tree problems are where recursion finally clicks for most people. Almost every binary-tree question reduces to the same move: do something with the current node, then recurse on its left and right subtrees and combine the results. Once you internalize that "solve the node, trust the recursion for the children" rhythm, depth, path sums, symmetry, and traversal problems all start to look alike.

These solutions cover the full interview range: the four traversals (preorder, inorder, postorder, level-order) and when each matters, depth and balance checks, lowest common ancestor, path-sum variants, and binary search tree properties like ordered inorder traversal and validation. We're explicit about the two ways to carry information through a tree — returning values up from children versus passing context down through parameters — because knowing which one a problem needs is usually the whole battle. Master this set and you'll also be better prepared for graphs, since a tree is just a graph without cycles.