LeetCode 114.Flatten Binary Tree to Linked List (二叉树展开为链表)

素颜马尾好姑娘i 2022-05-08 00:18 118阅读 0赞

题目描述：

给定一个二叉树，[原地][Link 1]将它展开为链表。

例如，给定二叉树

1
       / \
      2   5
     / \   \
    3   4   6

将其展开为：

1
     \
      2
       \
        3
         \
          4
           \
            5
             \
              6

AC C++ Solution:

/**
     * Definition for a binary tree node.
     * struct TreeNode {
     *     int val;
     *     TreeNode *left;
     *     TreeNode *right;
     *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
     * };
     */
    class Solution {
    public:
        void flatten(TreeNode* root) {
            TreeNode* now = root;
            while(now) {
                if(now->left)
                {
                    TreeNode *pre = now->left;
                    while(pre->right) {
                        pre = pre->right;
                    }
                    pre->right = now->right;        //将当前节点的右子树转接到左子节点的右叶节点上
                    now->right = now->left;         //将当前节点的右子树用左子树代替
                    now->left = NULL;
                }
                now = now->right;                   //遍历下一个节点
            }
        }
    };

类似的：

/**
     * Definition for a binary tree node.
     * struct TreeNode {
     *     int val;
     *     TreeNode *left;
     *     TreeNode *right;
     *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
     * };
     */
    class Solution {
    public:
        void flatten(TreeNode* root) {
            while(root) {
                if(root->left && root->right) {
                    TreeNode* t = root->left;
                    while(t->right)
                        t = t->right;
                    t->right = root->right;    //将当前节点的右子树接到左子树的右叶节点上
                }
                
                if(root->left)
                    root->right = root->left;  //再将当前节点的右子树替换为左子树
                root->left = NULL;
                root = root->right;      
            }
        }
    };

[Link 1]: https://baike.baidu.com/item/%E5%8E%9F%E5%9C%B0%E7%AE%97%E6%B3%95/8010757