樹是階層式的資料結構，由節點和邊組成。二元樹、二元搜尋樹 (BST) 是最常見的變體。遞迴是處理樹問題的核心技巧。

Notes:

  • 大多數樹的題目可以用 DFS（前序/中序/後序）或 BFS（層序遍歷）解決
  • BST 的中序遍歷會產生有序序列，這個性質非常有用
  • 遞迴解法要注意 base case 和回傳值的設計

跨倉庫導讀#

#94 Binary Tree Inorder Traversal #95 Unique Binary Search Trees II #96 Unique Binary Search Trees #98 Validate Binary Search Tree #100 Same Tree #101 Symmetric Tree #102 Binary Tree Level Order Traversal #103 Binary Tree Zigzag Level Order Traversal #104 Maximum Depth of Binary Tree #105 Construct Binary Tree from Preorder and Inorder Traversal #106 Construct Binary Tree from Inorder and Postorder Traversal #108 Convert Sorted Array to Binary Search Tree #110 Balanced Binary Tree #112 Path Sum #124 Binary Tree Maximum Path Sum #129 Sum Root to Leaf Numbers #144 Binary Tree Preorder Traversal #145 Binary Tree Postorder Traversal #173 Binary Search Tree Iterator #199 Binary Tree Right Side View #226 Invert Binary Tree #230 Kth Smallest Element in a BST #235 Lowest Common Ancestor of a Binary Search Tree #297 Serialize and Deserialize Binary Tree #337 House Robber III #427 Construct Quad Tree #450 Delete Node in a BST #513 Find Bottom Left Tree Value #538 Convert BST to Greater Tree #543 Diameter of Binary Tree #572 Subtree of Another Tree #606 Construct String From Binary Tree #617 Merge Two Binary Trees #652 Find Duplicate Subtrees #662 Maximum Width of Binary Tree #669 Trim a Binary Search Tree #701 Insert into a Binary Search Tree #783 Minimum Distance Between BST Nodes #894 All Possible Full Binary Trees #951 Flip Equivalent Binary Trees #958 Check Completeness of a Binary Tree #1376 Time Needed to Inform All Employees #1443 Minimum Time to Collect All Apples in a Tree #1448 Count Good Nodes in Binary Tree #1993 Operations On Tree