题解 | #牛群的树形结构展开#

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return TreeNode类
     */
    vector<int> nums;
    void inorder(TreeNode* root) {
        if (root == nullptr) return;
        nums.push_back(root->val);
        inorder(root->left);
        inorder(root->right);
    }
    TreeNode* flattenTree(TreeNode* root) {
        // write code here
        inorder(root);
        int len = nums.size();
        TreeNode* dummy = new TreeNode(-1);
        TreeNode* pre = dummy;
        for (int i = 0; i < len; i++) {
            TreeNode* t = new TreeNode(nums[i]);
            pre->right = t;
            pre = pre->right;
        }
        return dummy->right;
    }
};