day17打卡

1. 修剪二叉搜索树

/**

• 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 trimBST(TreeNode* root, int low, int high) {
  if(root == nullptr)
  {
  return nullptr;
  }
  if(root->val < low)
  {
  TreeNode *cur = root->right;

       TreeNode *right = trimBST(cur, low, high);
       return right;
   }
   if(root->val > high)
   {
       TreeNode *cur = root->left;
       
       TreeNode *left = trimBST(cur, low, high);
       return left;
  
   }
   root->left = trimBST(root->left, low, high);
   root->right = trimBST(root->right, low, high);
   return root;
  

  }
  };

2.将有序数组转化为二叉搜索树

/**

• 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 *traversal(vector& nums, int low, int high)
  {
  if(low <= high)
  {
  int mid = low + ((high - low) / 2);
  TreeNode root = new TreeNode(nums[mid]);
  root->left = traversal(nums, low, mid-1);
  root->right = traversal(nums, mid+1, high);
  return root;
  }
  return nullptr;
  }
  TreeNode sortedArrayToBST(vector& nums) {
  return traversal(nums, 0, nums.size()-1);
  }
  };

3.将二叉搜索树转化为累加树
/**

• 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 convertBST(TreeNode* root) {
  if(root == nullptr)
  {
  return nullptr;
  }
  root->right = convertBST(root->right);
  if(pre)
  {
  root->val += pre->val;
  }
  pre = root;
  root->left = convertBST(root->left);
  return root;
  }
  private:
  TreeNode *pre = nullptr;
  };