114. Flatten Binary Tree to Linked List

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 8  *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 9  *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
10  * };
11  */
12 class Solution {
13 public:
14     void flatten(TreeNode* root) {
15         if(root==NULL ||!root->left&&!root->right) return ; //因为此方法会对叶子节点进行，但没必要，所以加此条件去除操作叶子节点
16         if(root->left)flatten(root->left);
17         if(root->right)flatten(root->right);
18         TreeNode* temp = root->right;
19         root->right=root->left;
20         root->left=NULL;
21         while(root->right) root=root->right; //当新右子树很多结点时就需要循环到最后的一个右子树，再连接上去
22         root->right= temp;
23         
24     }
25 };