Flatten Binary Tree to Linked List

最新推荐文章于 2022-09-06 16:04:14 发布

cgdong2014

最新推荐文章于 2022-09-06 16:04:14 发布

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本文介绍了一种将二叉树结构通过特定算法展平为链表的方法。核心思路采用先序遍历的方式，将遍历到的节点依次连接起来形成链表。文章详细解释了具体的实现步骤及注意事项。

Given a binary tree, flatten it to a linked list in-place.

For example,
Given

The flattened tree should look like:

思路：基本思想就是用 preOrder 把TreeNode 放进一个 List 里面，然后取出来 left = null; right = next;

易错点：别忘记把left 设置成 null, 最后一个节点的right 也设置成null;

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

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public void flatten(TreeNode root) {
        if(root == null)
            return;
        ArrayList<TreeNode> list = new ArrayList<TreeNode>();
        preOrder(root, list);
        for(int i = 0; i < list.size() - 1; i++){
            list.get(i).left = null;
            list.get(i).right = list.get(i + 1);
        }
        list.get(list.size() - 1).left = null;
        list.get(list.size() - 1).right = null;
    }
    
    private void preOrder(TreeNode root, ArrayList<TreeNode> list){
        if(root == null)
            return;
        list.add(root);
        preOrder(root.left, list);
        preOrder(root.right, list);
    }
}