DFS

Preorder, inorder, postorder traversals recursively and iteratively.

6 min readMastering Data Structures & Algorithms for Software Engineering InterviewsCode

Recursive DFS

DFS pre-order traversal — watch the stack as nodes are visited

DFS Tree Traversal (pre-order)

Stack:1

Step 1 / 12 — Start: push root onto stack

Gothree-recursive-traversals.go

42 linesLn 1, Col 1Go

Closure captures result slice. Order of append determines traversal type. Simple and readable but uses O(h) call stack.

Iterative DFS

Use explicit stack. Preorder: push right then left (so left pops first). Inorder: traverse left while pushing, then process, go right. Postorder: modified preorder (root-right-left) then reverse.

Goiterative-traversals.go

56 linesLn 1, Col 1Go

Preorder: stack with right then left. Inorder: go left pushing, then process, go right. Postorder: root-right-left then reverse.

DFS Applications

Path sum: Root-to-leaf paths summing to target.
Max depth: Height of tree.
Diameter: Longest path between any two nodes.
Serialize/deserialize: Preorder with null markers.
LCA: Lowest common ancestor using recursion.
Tree symmetry: Mirror check with two pointers.

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