235. 二叉搜索树的最近公共祖先

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 
11 class Solution {
12 public:
13     TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
14         while(root){
15             if(p->val > root->val && q->val > root->val)  root = root->right;
16             else if(p->val < root->val && q->val < root->val)  root = root->left;
17             else return root;
18         }
19         return root;
20     }
21 };

701. 二叉搜索树中的插入操作

先查找符合条件的叶子结点，然后根据大小在这个节点下插入

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 8  *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 9  *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
10  * };
11  */
12 class Solution {
13 public:
14     TreeNode* deleteNode(TreeNode* root, int key) {
15         if(root == nullptr) return nullptr;
16         if(root->val == key){
17             if(root->left == nullptr)   return root->right;
18             if(root->right == nullptr)  return root->left;
19             TreeNode* result = root->left;
20             TreeNode* pre = root->left;
21             while(pre->right){
22                 pre = pre->right;
23             }
24             pre->right = root->right;
25             return result;
26         }
27         if(root->left == nullptr && root->right == nullptr && root->val != key){
28             return root;
29         }
30         if(root->val > key){
31             root->left = deleteNode(root->left, key);
32         }else{
33             root->right = deleteNode(root->right, key);
34         }
35         return root;
36     }
37 };

450. 删除二叉搜索树中的节点

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 8  *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 9  *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
10  * };
11  */
12 class Solution {
13 public:
14     TreeNode* insertIntoBST(TreeNode* root, int val) {
15         if(root == nullptr) return new TreeNode(val);
16         TreeNode* pre;
17         TreeNode* result = root;
18         while(root){
19             pre = root;
20             if(root->val > val){
21                 root = root->left;
22             }else{
23                 root = root->right;
24             }
25         }
26         if(val > pre->val)  pre->right = new TreeNode(val);
27         else pre->left = new TreeNode(val);
28         return result;
29     }
30 };