31. Flatten binary tree to linked list

Flatten binary tree to linked list

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

For example, given

         1        /        2   5      / \        3   4   6

 

The flattened tree shoshould 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

Thoughts:Such as hints.

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ TreeNode* getPreNode(TreeNode *root) {     if(root == NULL) return NULL;     while(root->right)  root = root->right;     return root; }class Solution {public:    void flatten(TreeNode *root) {        if(root == NULL) return;        TreeNode *pre = getPreNode(root->left);        if(pre) {         pre->right = root->right;         root->right = root->left;         root->left = NULL;        }        flatten(root->right);    }};

 

31. Flatten binary tree to linked list