day16打卡

1.二叉搜索树的最近公共祖先

/**

• 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 == nullptr)
{
return nullptr;
}
if(root->val > p->val && root->val > q->val)
{
return lowestCommonAncestor(root->left, p, q);
}
if(root->val < p->val && root->val < q->val)
{
return lowestCommonAncestor(root->right, p, q);
}
return root;
}
};

2. 二叉搜索树中的插入操作

class Solution {
public:
TreeNode* insertIntoBST(TreeNode* root, int val) {
if(root == nullptr)
{
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;
}
};

3. 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 == nullptr)
  {
  return nullptr;
  }
  if(root->val == key)
  {
  if(root->left == nullptr && root->right == nullptr)
  {
  delete root;
  return nullptr;
  }
  else if(root->left != nullptr && root->right == nullptr)
  {
  TreeNode *node = root->left;
  delete root;
  return node;
  }
  else if(root->left == nullptr && root->right != nullptr)
  {
  TreeNode *node = root->right;
  delete root;
  return node;
  }
  else
  {
  TreeNode *cur = root->right;
  //TreeNode tmp = root;
  while(cur->left != nullptr)
  {
  cur = cur->left;
  }
  cur->left = root->left;
  // delete tmp;
  // return cur;
  TreeNode tmp = root; // 把root节点保存一下，下面来删除
  root = root->right; // 返回旧root的右孩子作为新root
  delete tmp; // 释放节点内存（这里不写也可以，但C++最好手动释放一下吧）
  return root;
  }
  }
  if(root->val > key)
  {
  root->left = deleteNode(root->left, key);
  }
  if(root->val < key)
  {
  root->right = deleteNode(root->right, key);
  }
  return root;
  }
  };