代码随想录day23

538把二叉搜索树转化为累加树

class Solution {
public:
    TreeNode* convertBST(TreeNode* root) 
    {
        dg(root);
        return root;
    }
    int sum=0;
    void dg(TreeNode*root)
    {
        if(root==nullptr) return ;
        dg(root->right);
        sum+=root->val;
        root->val=sum;
        dg(root->left);
    }
};

669修剪二叉树

class Solution {
public:
    TreeNode* trimBST(TreeNode* root, int low, int high) {
        if(root==nullptr) return nullptr;
        if(root->valright,low,high);
        }
        if(root->val>high)
        {
            return trimBST(root->left,low,high);
        }
        root->left=trimBST(root->left,low,high);
        root->right=trimBST(root->right,low,high);
        return root;
    }
};

108 将有序数组转化为二叉树

class Solution {
public:
    TreeNode* sortedArrayToBST(vector& nums) 
    {
        TreeNode* node= sort(nums,0,nums.size()-1);
        return node;
    }
    TreeNode*sort (vector&nums,int l,int r)
    {
        if(l>r) return nullptr;
        int m=(l+r)/2;
        TreeNode*node= new TreeNode(nums[m]);
        node->left=sort(nums,l,m-1);
        node->right=sort(nums,m+1,r);
        return node;
    }
};