代码随想录算法训练营第22天|235. 二叉搜索树的最近公共祖先 701.二叉搜索树中的插入操作 450.删除二叉搜索树中的节点

235. 二叉搜索树的最近公共祖先

class Solution {
public:
    TreeNode* traversal(TreeNode* root, TreeNode* p, TreeNode* q) {
        if (root == NULL) return root;
        if (root->val > p->val && root->val > q->val) {
            TreeNode* left = traversal(root->left, p, q);
            if (left != NULL) return left;
        }
        if (root->val < p->val && root->val < q->val) {
            TreeNode* right = traversal(root->right, p, q);
            if (right != NULL) return right;
        }
        return root;
    }
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        TreeNode* res = traversal(root, p, q);
        return res;
    }
};

701.二叉搜索树中的插入操作

class Solution {
private:
    TreeNode* parent;
    void traversal(TreeNode* root, int val) {
        if (root == nullptr) {
            TreeNode* newNode = new TreeNode(val);
            if (val > parent->val) parent->right = newNode;
            else parent->left = newNode;
            return;
        }
        parent = root;
        if (val > root->val) traversal(root->right, val);
        if (val < root->val) traversal(root->left, val);
        return;
    }
public:
    TreeNode* insertIntoBST(TreeNode* root, int val) {
        if (root == nullptr) root = new TreeNode(val);
        traversal(root, val);
        return root;
    }
};

450.删除二叉搜索树中的节点

class Solution {
public:
    TreeNode* deleteNode(TreeNode* root, int key) {
        if (root == nullptr) return root;
        if (root->val == key) {
            if (root->left == nullptr && root->right == nullptr) {
                delete root;
                return nullptr;
            }else if (root->left != nullptr && root->right == nullptr) {
                auto retNode = root->left;
                delete root;
                return retNode;
            }else if (root->left == nullptr && root->right != nullptr) {
                auto retNode = root->right;
                delete root;
                return retNode;
            }else {
                TreeNode* cur = root->right;
                while (cur->left) cur = cur->left;
                cur->left = root->left;
                auto retNode = root->right;
                delete root;
                return retNode;
            }
        }
        if (root->val > key) root->left = deleteNode(root->left, key);
        if (root->val < key) root->right = deleteNode(root->right, key);
        return root;
    }
};