代码随想录算法训练营DAY18第六章 二叉树part06

目录

[530. 二叉搜索树的最小绝对差](#530. 二叉搜索树的最小绝对差)

[501. 二叉搜索树中的众数](#501. 二叉搜索树中的众数)

[236. 二叉树的最近公共祖先](#236. 二叉树的最近公共祖先)

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530. 二叉搜索树的最小绝对差

/**
 * 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 {
    void dfs(TreeNode* root,int& pre,int& ans){
        if(!root)return ;
        dfs(root->left,pre,ans);
        if(pre==-1)pre=root->val;
        else {
            ans=min(ans,root->val-pre);
            pre=root->val;
        }
        dfs(root->right,pre,ans);
    }
public:
    int getMinimumDifference(TreeNode* root) {
        int ans=INT_MAX;
        int pre=-1;
        dfs(root,pre,ans);
        return ans;
    }
};

501. 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 {
    int maxnum=0;
    unordered_map<int,int>map;
    void search(TreeNode* node) {
        if(!node)return;
        map[node->val]++;
        maxnum=max(maxnum,map[node->val]);
        search(node->left);
        search(node->right);
    }
public:
    vector<int> findMode(TreeNode* root) {
        search(root);
        vector<int> ans;
        for(auto& [key,value]:map){
            if(value==maxnum)ans.push_back(key);
        }
        return ans;
    }
};

236. 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* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(!root||root==p||root==q)return root;
        TreeNode* left=lowestCommonAncestor(root->left,p,q);
        TreeNode* right=lowestCommonAncestor(root->right,p,q);
        if(left&&right)return root;
        else if(left&&!right)return left;
        else if(!left&&right)return right;
        else return NULL;
    }
};