[LintCode] Flatten Binary Tree to Linked List 将二叉树展开成链表

最新推荐文章于 2025-08-22 01:16:35 发布

weixin_34415923

最新推荐文章于 2025-08-22 01:16:35 发布

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文章标签：数据结构与算法

本文介绍了一种将二叉树按照前序遍历的方式展平为类似链表结构的方法。通过三种不同的实现方式，包括使用栈、递归以及迭代的方法，详细解释了如何有效地完成这一转换过程。每种方法都注重于保持节点之间的正确连接，并确保不会出现时间或内存超限的问题。

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Flatten a binary tree to a fake "linked list" in pre-order traversal.

Here we use the right pointer in TreeNode as the next pointer in ListNode.

Notice

Don't forget to mark the left child of each node to null. Or you will get Time Limit Exceeded or Memory Limit Exceeded.

Example

              1
               \
     1          2
    / \          \
   2   5    =>    3
  / \   \          \
 3   4   6          4
                     \
                      5
                       \
                        6

LeetCode上的原题，请参见我之前的博客Flatten Binary Tree to Linked List。

解法一：

class Solution {
public:
    /**
     * @param root: a TreeNode, the root of the binary tree
     * @return: nothing
     */
    void flatten(TreeNode *root) {
        if (!root) return;
        stack<TreeNode*> s;
        s.push(root);
        while (!s.empty()) {
            TreeNode *t = s.top(); s.pop();
            if (t->left) {
                TreeNode *r = t->left;
                while (r->right) r = r->right;
                r->right = t->right;
                t->right = t->left;
                t->left = NULL;
            }
            if (t->right) s.push(t->right);
        }
    }
};

解法二：

class Solution {
public:
    /**
     * @param root: a TreeNode, the root of the binary tree
     * @return: nothing
     */
    void flatten(TreeNode *root) {
        if (!root) return;
        if (root->left) flatten(root->left);
        if (root->right) flatten(root->right);
        TreeNode *t = root->right;
        root->right = root->left;
        root->left = NULL;
        while (root->right) root = root->right;
        root->right = t;
    }
};

解法三：

class Solution {
public:
    /**
     * @param root: a TreeNode, the root of the binary tree
     * @return: nothing
     */
    void flatten(TreeNode *root) {
        TreeNode *cur = root;
        while (cur) {
            if (cur->left) {
                TreeNode * t = cur->left;
                while (t->right) t = t->right;
                t->right = cur->right;
                cur->right = cur->left;
                cur->left = NULL;
            }
            cur = cur->right;
        }
    }
};