114. 二叉树展开为链表

114. 二叉树展开为链表

给定一个二叉树，原地将它展开为链表。

例如，给定二叉树

    1
   / \
  2   5
 / \   \
3   4   6

将其展开为：

1
 \
  2
   \
    3
     \
      4
       \
        5
         \
          6

/**
 * 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;
        if(root.left != null){
            TreeNode pre = root.left;
            while(pre.right != null) pre = pre.right;
            pre.right = root.right;
            root.right = root.left;
            root.left = null;
        }
        flatten(root.right);
    }
}

改进：

/**
 * 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;
        while(root != null){
            if(root.left != null){
                TreeNode pre = root.left;
                while(pre.right != null) pre = pre.right;
                pre.right = root.right;
                root.right = root.left;
                root.left = null;
            }
            root = root.right;
        }
    }
}