Leetcode 114 Solution

This article provides solution to leetcode question 114 (flatten-binary-tree-to-linked-list)
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https://leetcode.com/problems/flatten-binary-tree-to-linked-list

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*& head, TreeNode*& tail)
    {
        if (root == NULL)
        {
            head = NULL;
            tail = NULL;
            return;
        }

        TreeNode *left_head, *left_tail, *right_head, *right_tail;

        flatten(root->left, left_head, left_tail);
        flatten(root->right, right_head, right_tail);

        head = root;
        TreeNode* curr = root;
        curr->left = NULL;

        if (left_head)
        {
            curr->right = left_head;
            curr = left_tail;
        }

        if (right_head)
        {
            curr->right = right_head;
            curr = right_tail;
        }

        tail = curr;
    }

    void flatten(TreeNode* root) {
        TreeNode *head, *tail;
        flatten(root, head, tail);
    }
};