114. 二叉树展开为链表

114. 二叉树展开为链表

---

题目链接：114. 二叉树展开为链表

代码如下：

/**
 * 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) {}
 * };
 */
 
 //先把各节点用先序遍历存储起来，然后依次连接即可
class Solution {
public:
    void flatten(TreeNode* root) {
        vector<TreeNode*> treeNodes;
        preOrder(root,treeNodes);

        for(int i=0;i<treeNodes.size();i++)
        {
            //不是最后一个节点
            if(i+1!=treeNodes.size())
            {
                treeNodes[i]->right=treeNodes[i+1];
            }
            else
            {
                treeNodes[i]->right=nullptr;
            }
            treeNodes[i]->left=nullptr;
        }

    }

    //前序递归
    void preOrder(TreeNode* root,vector<TreeNode*>& treeNodes)
    {
        if(root==nullptr)
            return;
    
        treeNodes.push_back(root);
        preOrder(root->left,treeNodes);
        preOrder(root->right,treeNodes);
    }
};