68. 树中两个节点的最低公共祖先

https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-search-tree/

//注意是二叉搜索树
class Solution {
public:
    TreeNode* ans;
    void dfs(TreeNode* root, TreeNode* p, TreeNode* q){
        if(root->val > p->val && root->val > q->val){
            ans = root;
            dfs(root->left, p, q);
        }else if(root->val < p->val && root->val < q->val){
            ans = root;
            dfs(root->right, p, q);
        }else{
            ans = root;
            return ;
        }
    }
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        dfs(root, p, q);
        return ans;
    }
};