leetcode114. Flatten Binary Tree to Linked List

/**
 * 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;
                now->right = now->left;
                now->left = NULL;
            }
            now = now->right;
        }
    }
};

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