1. 二叉搜索树的最近公共祖先
给定一个二叉搜索树, 找到该树中两个指定节点的最近公共祖先。
方法一：

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def lowestCommonAncestor(root, p, q):
    if p.val > q.val:
        temp = p
        p = q
        q = temp
    while root is not None:
        if root.val < p.val:
            root = root.right
        elif root.val > q.val:
            root = root.left
        else:
            break
    return root

方法二：

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def lowestCommonAncestor(root, p, q):
    if root.val < p.val and root.val < q.val:
        return lowestCommonAncestor(root.right, p, q)

    if root.val > p.val and root.val > q.val:
        return lowestCommonAncestor(root.left, p, q)
    return root