代码随想录算法训练营第23天

今日刷题3道：669. 修剪二叉搜索树，108.将有序数组转换为二叉搜索树，538.把二叉搜索树转换为累加树。

●  669. 修剪二叉搜索树

题目链接/文章讲解： https://programmercarl.com/0669.%E4%BF%AE%E5%89%AA%E4%BA%8C%E5%8F%89%E6%90%9C%E7%B4%A2%E6%A0%91.html

视频讲解： https://www.bilibili.com/video/BV17P41177ud

class Solution {

public:

    TreeNode* trimBST(TreeNode* root, int low, int high) {

        if(root==nullptr) return nullptr;

        if(root->val < low){

            TreeNode* right = trimBST(root->right,low,high);

            return right;

        }

        if(root->val > high){

            TreeNode* left = trimBST(root->left,low,high);

            return left;

        }

        root->left =trimBST(root->left,low,high);

        root->right=trimBST(root->right,low,high);

        return root;

    }

};

●  108.将有序数组转换为二叉搜索树

https://programmercarl.com/0108.%E5%B0%86%E6%9C%89%E5%BA%8F%E6%95%B0%E7%BB%84%E8%BD%AC%E6%8D%A2%E4%B8%BA%E4%BA%8C%E5%8F%89%E6%90%9C%E7%B4%A2%E6%A0%91.html

视频讲解：https://www.bilibili.com/video/BV1uR4y1X7qL

class Solution {

private:

    TreeNode* traversal(vector<int>& nums, int left, int right){

        if(left > right) return nullptr;

        int mid = left + (right - left)/2;

        TreeNode* root = new TreeNode(nums[mid]);

        root->left = traversal(nums,left,mid-1);

        root->right = traversal(nums,mid+1,right);

        return root;

    }

public:

    TreeNode* sortedArrayToBST(vector<int>& nums) {

        TreeNode* root = traversal(nums,0,nums.size()-1);

        return root;

    }

};

●  538.把二叉搜索树转换为累加树

https://programmercarl.com/0538.%E6%8A%8A%E4%BA%8C%E5%8F%89%E6%90%9C%E7%B4%A2%E6%A0%91%E8%BD%AC%E6%8D%A2%E4%B8%BA%E7%B4%AF%E5%8A%A0%E6%A0%91.html

视频讲解：https://www.bilibili.com/video/BV1d44y1f7wP

class Solution {

private:

    int pre=0;

    void traversal(TreeNode* cur){

        if(cur==NULL) return;

        traversal(cur->right);

        cur->val+=pre;

        pre = cur->val;

        traversal(cur->left);

    }

public:

    TreeNode* convertBST(TreeNode* root) {

        pre=0;

        traversal(root);

        return root;

    }

};