Leetcode 236 Lowest Common Ancestor of a Binary Tree

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.

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).”

        _______3______

       /              \

    ___5__          ___1__

   /      \        /      \

   6      _2       0       8

         /  \

         7   4

For example, the lowest common ancestor (LCA) of nodes 5 and 1 is 3. Another example is LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.

如果root为LCA则返回root，否则检测左子树与右子树，如果其中有一个为LCA则返回，如果两边都不是LCA则返回NULL。

class Solution:

    # @param {TreeNode} root

    # @param {TreeNode} p

    # @param {TreeNode} q

    # @return {TreeNode}

    def lowestCommonAncestor(self, root, p, q):

        if not root or root == p or root == q: return root

        left, right = self.lowestCommonAncestor(root.left, p, q), self.lowestCommonAncestor(root.right, p, q)

        return root if left and right else left or right