114. Flatten Binary Tree to Linked List

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public void flatten(TreeNode root) {
        if (root == null) {
            return;
        }
        flatten(root.left);
        flatten(root.right);
        
        if (root.left != null) {
            TreeNode temp = root.right;
            root.right = root.left;
            root.left = null;
            TreeNode cur = root;
            while (cur.right != null) {
                cur = cur.right;
            }
            cur.right = temp;
        }
    }
    
}