Flatten Binary Tree to Linked List

最新推荐文章于 2022-09-06 16:04:14 发布

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本文介绍了如何使用递归和栈实现将二叉树转换为链表的操作，确保每一步操作都清晰明了，特别强调了在处理每个节点时将左子节点设置为null的小技巧。

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

For example,
Given

The flattened tree should look like:

click to show hints.

Hints:

If you notice carefully in the flattened tree, each node's right child points to the next node of a pre-order traversal.

Have you been asked this question in an interview?

这道题目用stack 或者recursive 实现 preorder traversal
有一个小细节要注意，就是在对每个TreeNode 处理的时候，要记得把他们的左结点设为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;
        }
        Stack<TreeNode> st = new Stack<TreeNode>();
        st.push(root);
        TreeNode cur;
        TreeNode dummy = new TreeNode(0);
        TreeNode pre = dummy;
        while (!st.empty()) {
            cur = st.pop();
            if (cur.right != null) {
                st.push(cur.right);
            } if (cur.left != null) {
                st.push(cur.left);
            }
            cur.left = null;
            pre.right = cur;
            pre = pre.right;
        }
    }
}