Process node and recursively visit children in specific order

function dfs(node) { if(!node) return; process(node); dfs(node.left); dfs(node.right); }

Use queue to process nodes level by level from top to bottom

queue = [root]; while(queue.length) { node = queue.shift(); process(node); if(node.left) queue.push(node.left); if(node.right) queue.push(node.right); }

Solve problem by combining solutions from left and right subtrees

function solve(node) { if(!node) return baseCase; left = solve(node.left); right = solve(node.right); return combine(left, right, node); }

Maintain current path during traversal to check conditions

function findPath(node, path) { if(!node) return; path.push(node.val); if(isLeaf(node)) checkCondition(path); findPath(node.left, path); findPath(node.right, path); path.pop(); }

Build tree from traversal arrays or serialized format

function buildTree(inorder, preorder) { if(!preorder.length) return null; root = new Node(preorder[0]); idx = inorder.indexOf(root.val); root.left = buildTree(inorder.slice(0,idx), preorder.slice(1,idx+1)); root.right = buildTree(inorder.slice(idx+1), preorder.slice(idx+1)); return root; }

Compare two trees node by node with synchronized traversal

function isSame(p, q) { if(!p && !q) return true; if(!p || !q) return false; return p.val === q.val && isSame(p.left, q.left) && isSame(p.right, q.right); }