LeetCode 刷题： 两个二叉树节点的最近公共节点Least Common Ancestor

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.

/** * 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)            return nullptr;                if(root == p || root == q)            return root;                TreeNode* left_side = lowestCommonAncestor(root->left, p, q);        TreeNode* right_side = lowestCommonAncestor(root->right, p, q);                    if(left_side && right_side)            return root;                    if(left_side)            return left_side;                if(right_side)            return right_side;        return nullptr;    }};