LeetCode: Flatten Binary Tree to Linked List

Flatten Binary Tree to Linked List

 Total Accepted: 23135 Total Submissions: 82181My Submissions

Given a binary tree, flatten it to a linked list in-place.

For example,
Given

         1        / \       2   5      / \   \     3   4   6

The flattened tree should look like:

   1    \     2      \       3        \         4          \           5            \             6

click to show hints.

Hints:

If you notice carefully in the flattened tree, each node's right child points to the next node of a pre-order traversal.

/** * Definition for binary tree * 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 != NULL){            TreeNode* temp = root->right;            root->right = root->left;            root->left = NULL;            TreeNode* p = root;            while(p->right){                p = p->right;            }            p->right = temp;            root = root->right;        }                    }};

Round 2:

class Solution {public:    void flatten(TreeNode *root) {         preOrder(root);    }private:TreeNode *preOrder(TreeNode *node){if(node == NULL)return NULL;TreeNode *temp = node->right;TreeNode *root = node;if(node->left != NULL){node->right = preOrder(node->left);node->left = NULL;while(node->right != NULL)node = node->right;}node->right = preOrder(temp);return root;}};