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Commit 7e8f781

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solves flatten multilevel doubly linked list
1 parent fec4381 commit 7e8f781

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‎README.md

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| 414 | [Third Maximum Number](https://leetcode.com/problems/third-maximum-number) | [![Java](assets/java.png)](src/ThirdMaximumNumber.java) [![Python](assets/python.png)](python/fizz_buzz.py) | |
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| 415 | [Add Strings](https://leetcode.com/problems/add-strings) | [![Java](assets/java.png)](src/AddString.java) [![Python](assets/python.png)](python/add_strings.py) | |
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| 422 | 🔒 [Valid Word Square](https://leetcode.com/problems/valid-word-square) | | |
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| 430 | [Flatten a Multilevel Doubly Linked List](https://leetcode.com/problems/flatten-a-multilevel-doubly-linked-list) | [![Java](assets/java.png)](src/FlattenAMultiLevelDoublyLinkedList.java) | |
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| 434 | [Number of Segments in a String](https://leetcode.com/problems/number-of-segments-in-a-string) | [![Java](assets/java.png)](src/NumberOfSegmentsInString.java) [![Python](assets/python.png)](python/number_of_segments_in_a_string.py) | |
290291
| 441 | [Arranging Coins](https://leetcode.com/problems/arranging-coins) | [![Java](assets/java.png)](src/ArrangingCoins.java) [![Python](assets/python.png)](python/arranging_coins.py) | |
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| 443 | [String Compression](https://leetcode.com/problems/string-compression) | [![Java](assets/java.png)](src/StringCompression.java) [![Python](assets/python.png)](python/string_compression.py) | |
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// T: O(n)
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// S: O(n)
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public class FlattenAMultiLevelDoublyLinkedList {
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private static final class Node {
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public int val;
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public Node prev;
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public Node next;
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public Node child;
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}
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public Node flatten(Node head) {
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for (Node temp = head ; temp != null ; temp = temp.next) {
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if (temp.child != null) {
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Node lastNodeOfFlattenedChildren = flattenLinkedList(temp.child);
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lastNodeOfFlattenedChildren.next = temp.next;
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if (temp.next != null) {
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temp.next.prev = lastNodeOfFlattenedChildren;
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}
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temp.next = temp.child;
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temp.child.prev = temp;
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temp.child = null;
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}
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}
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return head;
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}
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private Node flattenLinkedList(Node head) {
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Node temp = head;
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for (; temp.next != null ; temp = temp.next) {
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if (temp.child != null) {
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Node lastNodeOfFlattenedChildren = flattenLinkedList(temp.child);
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lastNodeOfFlattenedChildren.next = temp.next;
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temp.next.prev = lastNodeOfFlattenedChildren;
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temp.next = temp.child;
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temp.child.prev = temp;
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temp.child = null;
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}
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}
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if (temp.child != null) {
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Node lastNodeOfFlattenedChildren = flattenLinkedList(temp.child);
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temp.next = temp.child;
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temp.child.prev = temp;
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temp.child = null;
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return lastNodeOfFlattenedChildren;
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}
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return temp;
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}
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}

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