Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.
According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”
_______6______
/ \
___2__ ___8__
/ \ / \
0 _4 7 9
/ \
3 5
For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.
通过观察可以发现，如果p和q分别位于root的两侧，那么root就是他们的LCA。否则的话，判断一下LCA应该是在左边还是在右边。注意L11 L13的return不能缺，因为这里并不是在调用这个函数，而是在递归定义。
def lowestCommonAncestor(self, root, p, q):
"""
:type root: TreeNode
:type p: TreeNode
:type q: TreeNode
:rtype: TreeNode
"""
if (p.val <= root.val and q.val >= root.val) or (p.val >= root.val and q.val <= root.val):
return root
elif p.val < root.val:
return self.lowestCommonAncestor(root.left, p, q)
else:
return self.lowestCommonAncestor(root.right, p, q)