day23 - 二叉树part09

669. 修剪二叉搜索树

详解

/**
 * 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 {
public:
    TreeNode* trimBST(TreeNode* root, int low, int high) {
        if(!root) return nullptr;
        if(root->val < low) return trimBST(root->right, low, high);
        if(root->val > high) return trimBST(root->left, low, high);

        root->left = trimBST(root->left, low, high); // root->left接入符合条件的左孩子
        root->right = trimBST(root->right, low, high); // root->right接入符合条件的右孩子
        return root;
    }
};

108. 将有序数组转换为二叉搜索树

/**
 * 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 {
public:
    TreeNode* search(vector<int> nums, int left, int right){
        if(left>right) return nullptr;
        int mid = (right + left)/2;
        TreeNode* node = new TreeNode(nums[mid]);
        node->left = search(nums, left, mid-1);
        node->right = search(nums, mid+1, right);
        return node;
    }

    TreeNode* sortedArrayToBST(vector<int>& nums) {
        return search(nums, 0, nums.size() - 1);
    }
};

538. 把二叉搜索树转换为累加树

/**
 * 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 {
public:
    TreeNode* pre = NULL;
    TreeNode* convertBST(TreeNode* root) {
        if(!root) return nullptr;

        root->right = convertBST(root->right);

        if(pre) root->val += pre->val;

        pre = root;

        root->left = convertBST(root->left);

        return root;
    }
};