day22 - 二叉树part08

235. 二叉搜索树的最近公共祖先

详解

/**
 * 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 NULL;
        if(root->val >= p->val && root->val <= q->val) return root;
        if(root->val >= q->val && root->val <= p->val) return root;

        TreeNode* left = lowestCommonAncestor(root->left, p, q);
        TreeNode* right =lowestCommonAncestor(root->right, p, q);
        return left? left:right;
    }
};

701. 二叉搜索树中的插入操作

/**
 * 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 == NULL) {
            TreeNode* node = new TreeNode(val);
            return node;
        }
        if (root->val > val) root->left = insertIntoBST(root->left, val);
        if (root->val < val) root->right = insertIntoBST(root->right, val);
        return root;
    }
};

 

450. 删除二叉搜索树中的节点

/**
 * 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* deleteNode(TreeNode* root, int key) {
        if(!root) return root;

        if(root->val == key){
            if(!root->left && !root->right){
                delete root;
                return nullptr;
            }else if(!root->left){
                TreeNode* node = root->right;
                delete root;
                return node;
            }else if(!root->right){
                TreeNode* node = root->left;
                delete root;
                return node;
            }else{
                // 第五种情况：左右孩子节点都不为空，则将删除节点的左子树放到删除节点的右子树的最左面节点的左孩子的位置
                // 并返回删除节点右孩子为新的根节点。
                TreeNode* cur = root->right;
                while(cur->left != nullptr)
                    cur = cur->left;
                cur->left = root->left;
                return root->right;
            }
        }
        if(root->val > key) root->left = deleteNode(root->left, key);
        if(root->val < key) root->right = deleteNode(root->right, key);
        return root;
    }
};