114 Flatten Binary Tree to Linked List

最新推荐文章于 2024-01-17 15:25:50 发布

dongbeier

最新推荐文章于 2024-01-17 15:25:50 发布

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分类专栏： MicroSoft LeetCode

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本文介绍了一种将二叉树结构通过算法转换为链表的方法，使用递归和迭代两种方式实现。该算法首先检查二叉树节点是否为空，然后分别处理左子树和右子树，最后调整节点的左右指针来完成转换。

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

For example, given the following tree:

The flattened tree should look like:

递归:

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

迭代:

/**
 * 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;
        Stack<TreeNode> s= new Stack<>();
        s.push(root);
        
        while (!s.isEmpty()) {
            TreeNode node = s.pop();
            if (node.right != null) {
                s.push(node.right);
            }
            if (node.left != null) {
                s.push(node.left);
            }
            if (!s.isEmpty()) {
                node.right = s.peek();
            }
            node.left = null;
        }
    }
}