day15

1. 二叉搜素树的最小绝对差

/**

• 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:
  Solution()
  :min(INT_MAX), pre(nullptr)
  {
  }
  void traversal(TreeNode cur)
  {
  if(cur == nullptr)
  {
  return;
  }
  traversal(cur->left);
  if(pre != nullptr)
  {
  if(min > cur->val - pre->val)
  {
  min = cur->val - pre->val;
  }
  }
  pre = cur;
  traversal(cur->right);
  }
  int getMinimumDifference(TreeNode root)
  {
  traversal(root);
  return min;
  }
  private:
  int min;
  TreeNode *pre;
  };

2. 二叉搜索树中的众数

/**

• 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:
  void traversal(TreeNode *cur)
  {
  if(cur == nullptr)
  {
  return;
  }
  traversal(cur->left);
  if(pre != nullptr)
  {
  if(pre->val == cur->val)
  {
  ++num;

   if(num > max)
   {
       max = num;
       value.clear();
       value.push_back(pre->val);
   }
   if(num == max)
   {
       value.push_back(pre->val);
   }
       }
       else
       {
           num = 1;
       }
   }
   else
   {
       num = 1;
   }
   pre = cur;
   
   traversal(cur->right);
  

  }
  vector findMode(TreeNode* root) {
  value.clear();
  traversal(root);
  return value;
  }
  private:
  int max = 0;
  int num = 0;
  vector value;
  TreeNode *pre = nullptr;
  };

3. 二叉树的最近公共祖先

   /**

• 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 traversal(TreeNode *root, TreeNode p, TreeNode q)
  {
  if(root == nullptr)
  {
  return nullptr;
  }
  if(root == p || root == q)
  {
  return root;
  }
  TreeNode left = traversal(root->left, p, q);
  TreeNode right = traversal(root->right, p, q);
  if(left != nullptr && right != nullptr)
  {
  return root;
  }
  else if(left != nullptr && right == nullptr)
  {
  return left;
  }
  else if(left == nullptr && right != nullptr)
  {
  return right;
  }
  else
  {
  return nullptr;
  }
  }
  TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q)
  {
  return traversal(root, p ,q);
  }
  };