【LeetCode】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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本文介绍了一种将二叉树结构通过特定算法转换为链表的方法，并提供了详细的实现步骤与代码示例。

Flatten Binary Tree to Linked List

Total Accepted: 18516 Total Submissions: 66328 My Submissions

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.

这种题需要使用传引用，得出一个头和尾结点，这样递归起来非常简单。中间需要对NULL多作判断

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void flatten(TreeNode *root) {
        if(root == NULL)
            return;
        TreeNode *head = NULL, *tail = NULL;
        flattenHelper(root,head,tail);
        root = head;
    }
    void flattenHelper(TreeNode *root, TreeNode *&head, TreeNode *&tail) {
        if (root == NULL) {
            head = NULL;
            tail = NULL;
            return;/////////////////////////////////////////
        }
        head = tail = root;//!!!!
        TreeNode *left_head = NULL, *left_tail = NULL, *right_head = NULL, *right_tail = NULL;
        if(root->left) {
            flattenHelper(root->left,left_head,left_tail);
        }
        if(root->right) {
            flattenHelper(root->right,right_head,right_tail);
        }
        if (left_head) {//!!!!
            root->right = left_head;
            root->left = NULL;
        }
        else {
            left_tail = root;//!!!!
        }
        tail = left_tail;
        if (right_head) {//!!!!
            left_tail->right = right_head;
        }
        else {
            right_tail = left_tail;//!!!!
        }
        tail = right_tail;
    }
};