二叉树的最近公共祖先

[题目](235. 二叉搜索树的最近公共祖先)

重点

需要利用二叉搜索树的特性

代码实现

/**
 * 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 {
private:
    TreeNode* traversal(TreeNode* cur, TreeNode* p, TreeNode* q) {
        if (cur == NULL) {
            return cur;
        }
        // 左
        if (cur->val > p->val && cur->val > q->val) {
            TreeNode* left = traversal(cur->left, p, q);
            if (left) {
                return left;
            }
        }
        // 右
        if (cur->val < p->val && cur->val < q->val) {
            TreeNode* right = traversal(cur->right, p, q);
            if (right) {
                return right;
            }
        }
        return cur;
    }
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        return traversal(root, p, q);
    }
};

二叉搜索树中的插入操作

[题目](701. 二叉搜索树中的插入操作)

重点

插入节点到叶子节点

代码实现

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* insertIntoBST(TreeNode* root, int val) {
        if (!root) {
            return new TreeNode(val);
        }
        if (root->val > val) {
            root->left = insertIntoBST(root->left, val);
        }
        if (root->val < val) {
            root->right = insertIntoBST(root->right, val);
        }
        return root;
    }
};