LeetCode/114. Flatten Binary Tree to Linked List at main · raiden-02/LeetCode · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
//O(N) time O(N) space Intuitive
/**
 * 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 {
    vector<int> arr;

    void helper(TreeNode *root) {
        if(not root)
            return;

        arr.push_back(root->val);

        helper(root->left), helper(root->right);
    }
public:
    void flatten(TreeNode* root) {
        if(not root)
            return;

        helper(root);

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

        for(int i = 1; i < arr.size(); i++)
            tmp->right = new TreeNode(arr[i]), tmp = tmp->right;

    }
};

//O(N) time O(1) space morris traversal
/**
 * 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:
    //morris traversal
    void flatten(TreeNode* root) {
        TreeNode *prev;

        while(root) {
            if(not root->left) {
                root = root->right;
                continue;
            }

            prev = root->left;

            while(prev->right)
                prev = prev->right;

            prev->right = root->right;
            root->right = root->left;
            root->left = nullptr;

            root = root->right;
        }
    }
};