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，原地将它展开为一个单链表。

例如，给定二叉树

    1
   / \
  2   5
 / \   \
3   4   6
将其展开为：

1
 \
  2
   \
    3
     \
      4
       \
        5
         \
          6

寻找前驱节点

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

右左根来遍历

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    TreeNode last = null;
    public void flatten(TreeNode root) {
        if(root==null){
            return;
        }   
        flatten(root.right);
        flatten(root.left);
        root.right = last;
        root.left = null;
        last = root;
    }

}

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/flatten-binary-tree-to-linked-list
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