[数据结构与算法]LeetCode 114. 二叉树展开为链表

题目描述

114. 二叉树展开为链表

解法：

递归，看下图就懂了，先压左边，再压右边，最后回到根结点上将原先的右子树接到当前右子树的末端

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    void flatten(TreeNode* root) {
        if (root == nullptr) return;
        
        flatten(root->left);
        flatten(root->right);

        TreeNode* left = root->left;
        TreeNode* right = root->right;
        root->left = nullptr;
        root->right = left;

        TreeNode* p = root;
        while (p->right != nullptr) p = p->right;
        p->right = right;
        

    }
};