LeetCode 236. Lowest Common Ancestor of a Binary Tree

题目链接：https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/#/description

题目描述：

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.

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:   TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {    if (!root || root == p || root == q) return root;    TreeNode* left = lowestCommonAncestor(root->left, p, q);    TreeNode* right = lowestCommonAncestor(root->right, p, q);    return !left ? right : !right ? left : root;    }};