235. Lowest Common Ancestor of a Binary Search Tree

O(h)

/**
 * 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 (!p || !q) return root;
        auto [s, l] = minmax(p->val, q->val);
        if (s <= root->val && root->val <= l) return root; // 注意等于的case，说明p和q一个是另一个的父节点
        if (root->val < s) return lowestCommonAncestor(root->right, p, q);
        if (l < root->val) return lowestCommonAncestor(root->left, p, q);
        return nullptr;
    }
};

/**
 * 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) {
        auto [lo, hi] = minmax(p->val, q->val);
        if (lo <= root->val && root->val <= hi) return root;
        return hi < root->val ? lowestCommonAncestor(root->left, p, q) : lowestCommonAncestor(root->right, p, q);
    }
};