427- binary tree (617. merge binary tree, 700. search in binary search tree, 98. verify binary search tree, 530. minimum absolute difference of binary search tree)

617. Merge binary tree

class Solution {
    
public:
    TreeNode* mergeTrees(TreeNode* root1, TreeNode* root2) {
    
        if (root1 == nullptr)    return root2;
        if (root2 == nullptr)    return root1;

        root1->val += root2->val;

        root1->left = mergeTrees(root1->left, root2->left);
        root1->right = mergeTrees(root1->right, root2->right);
        return root1;
    }
};

700. Search in binary search tree

class Solution {
    
public:
    TreeNode* searchBST(TreeNode* root, int val) {
    
        if (root == nullptr || root->val == val) return root;

        if (root->val > val) return searchBST(root->left, val);
        if (root->val < val) return searchBST(root->right, val);

        return nullptr;
    }
};

98. Verify binary search tree

class Solution {
    
private:
    vector<int> res;

    void traversal(TreeNode* root)
    {
    
        if (root == nullptr)    return;

        traversal(root->left);
        res.push_back(root->val);
        traversal(root->right);
    }
public:
    bool isValidBST(TreeNode* root) {
    
        res.clear();
        traversal(root);


        for (int i = 1; i < res.size(); i++)
        {
    
            if (res[i - 1] < res[i])
            {
    
                continue;
            }
            else
            {
    
                return false;
            }
        }
        return true;
    }
};

530. The minimum absolute difference of binary search tree

class Solution {
    
private:
    vector<int> res;

    void traversal(TreeNode* root)
    {
    
        if (root == nullptr) return;

        traversal(root->left);
        res.push_back(root->val);
        traversal(root->right);
    }
public:
    int getMinimumDifference(TreeNode* root) {
    
        res.clear();
        traversal(root);
        if (res.size() < 2)  return 0;
        int result = INT_MAX;
        for (int i = 1; i < res.size(); i++)
        {
    
            result = std::min(result, res[i] - res[i - 1]);
        }

        return result;
    }
};