代码随想录Day21

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LeetCode669.修剪二叉搜索树

class Solution {
public:
    TreeNode* trimBST(TreeNode* root, int low, int high) {
        if(!root)return nullptr;
        while(root && (root->val < low || root->val >high)){
            if(root->val < low){
                root = root->right;
            }else if(root->val >high){
                root = root->left;
            }
        }
        if(!root)return nullptr;
        root->left = trimBST(root->left, low, high);
        root->right = trimBST(root->right, low, high);
        return root;
    }
};

LeetCode108.将有序数组转化为二叉搜索树

class Solution {
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        TreeNode* root;
        if(nums.size() == 1){
            root = new TreeNode(nums[0]);
            return root;
        }else if(nums.empty()){
            root = nullptr;
            return root;
        }else{
            int midIndex = nums.size()/2;
            root = new TreeNode(nums[midIndex]);
            vector<int> leftnums(nums.begin(), nums.begin() + midIndex);
            vector<int> rightnums(nums.begin() + midIndex + 1, nums.end());
            root->left = sortedArrayToBST(leftnums);
            root->right = sortedArrayToBST(rightnums);
            return root;
        }
    }
};

LeetCode538.把二叉搜索树转化为二叉累加树

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

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