Leetcode-Problems/114. Flatten Binary Tree to Linked List at master · alexkoby/Leetcode-Problems · 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
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public void flatten(TreeNode root) {
        if(root != null){
            flattenReturnLast(root);
        }
        else{
            return;
        }

    }

    public TreeNode flattenReturnLast(TreeNode root){
        if(root.left != null && root.right != null){
            TreeNode returnValue = flattenReturnLast(root.right);
            TreeNode leftReturn = flattenReturnLast(root.left);
            leftReturn.right = root.right;
            root.right = root.left;
            root.left = null;
            return returnValue;
        }
        else if(root.left == null && root.right != null){
            return flattenReturnLast(root.right);
        }
        else if(root.left != null && root.right == null){
            TreeNode returnValue = flattenReturnLast(root.left);
            root.right = root.left;
            root.left = null;
            return returnValue;
        }
        else{//both are null
            return root;
        }
    }
}