首发于 语雀文档@blueju

    代码：

    1. /**
    2.  * Definition for a binary tree node.
    3.  * class TreeNode {
    4.  *     val: number
    5.  *     left: TreeNode | null
    6.  *     right: TreeNode | null
    7.  *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
    8.  *         this.val = (val===undefined ? 0 : val)
    9.  *         this.left = (left===undefined ? null : left)
    10.  *         this.right = (right===undefined ? null : right)
    11.  *     }
    12.  * }
    13.  */
    14. function lowestCommonAncestor(root: TreeNode | null, p: TreeNode | null, q: TreeNode | null): TreeNode | null {
    15.     const dfs = (root: TreeNode | null, p: TreeNode | null, q: TreeNode | null): TreeNode | null => {
    16.         if (root === null) return root
    17.         if (root === p || root === q) return root
    18.         if ((p.val < root.val) && (q.val < root.val)) {
    19.             return dfs(root.left, p, q)
    20.         }
    21.         if ((p.val > root.val) && (q.val > root.val)) {
    22.             return dfs(root.right, p, q)
    23.         }
    24.         return root
    25.     }
    26.     return dfs(root, p, q)
    27. };