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anishLearnsToCodeanishLearnsToCode
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solves #25: Reverse Nodes in k-Group in java
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‎README.md

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| 21 | [Merge 2 Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/) | [![Java](assets/java.png)](src/Merge2SortedLists.java) [![Python](assets/python.png)](python/merge_2_sorted_lists.py) | |
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| 22 | [Generate Parentheses](https://leetcode.com/problems/generate-parentheses) | [![Java](assets/java.png)](src/GenerateParentheses.java) | |
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| 24 | [Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs) | [![Java](assets/java.png)](src/SwapNodesInPairs.java) | |
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| 25 | [Reverse Nodes in k-Group](https://leetcode.com/problems/reverse-nodes-in-k-group) | [![Java](assets/java.png)](src/ReverseNodesInKGroup.java) | |
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| 26 | [Remove Duplicates From Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array) | [![Java](assets/java.png)](src/RemoveDuplicatesFromSortedArray.java) [![Python](assets/python.png)](python/remove_duplicates_from_sorted_array.py) [![js](assets/javascript.png)](javascript/RemoveDuplicatesFromSortedArray.js) | |
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| 27 | [Remove Element](https://leetcode.com/problems/remove-element/) | [![Java](assets/java.png)](src/RemoveElement.java) [![Python](assets/python.png)](python/remove_element.py) | |
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| 28 | [Needle in Haystack](https://leetcode.com/problems/implement-strstr) | [![Java](assets/java.png)](src/NeedleInHaystack.java) [![Python](assets/python.png)](python/needle_in_haystack.py) | |

‎src/CopyListWithRandomPointer.java

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@@ -6,7 +6,7 @@
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import java.util.Map;
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public class CopyListWithRandomPointer {
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private static final class Node {
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public static final class Node {
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int val;
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Node next;
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Node random;
@@ -18,7 +18,7 @@ public Node(int val) {
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}
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}
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public HelloWorld.Node copyRandomList(HelloWorld.Node head) {
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public Node copyRandomList(Node head) {
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if (head == null) {
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return null;
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}
@@ -29,26 +29,26 @@ public HelloWorld.Node copyRandomList(HelloWorld.Node head) {
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}
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// A->B->C --> A->A'->B->B'
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private static void createWeavedList(HelloWorld.Node head) {
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for (HelloWorld.Node i = head; i != null ; i = i.next.next) {
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HelloWorld.Node newNode = new HelloWorld.Node(i.val);
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private static void createWeavedList(Node head) {
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for (Node i = head; i != null ; i = i.next.next) {
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Node newNode = new Node(i.val);
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newNode.next = i.next;
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i.next = newNode;
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}
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}
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private static void linkRandomPointersForNewNodes(HelloWorld.Node head) {
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for (HelloWorld.Node i = head; i != null ; i = i.next.next) {
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private static void linkRandomPointersForNewNodes(Node head) {
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for (Node i = head; i != null ; i = i.next.next) {
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if (i.random == null) {
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continue;
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}
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i.next.random = i.random.next;
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}
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}
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private static HelloWorld.Node unweaveList(HelloWorld.Node head) {
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final HelloWorld.Node pointerNew = head.next;
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for (HelloWorld.Node old = head, i = head.next; i != null && old != null ; i = i.next, old = old.next) {
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private static Node unweaveList(Node head) {
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final Node pointerNew = head.next;
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for (Node old = head, i = head.next; i != null && old != null ; i = i.next, old = old.next) {
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old.next = old.next == null ? null : old.next.next;
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i.next = i.next == null ? null : i.next.next;
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}

‎src/HelloWorld.java

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@@ -1,67 +1,35 @@
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public class HelloWorld {
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public static class Node {
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int val;
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Node next;
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Node random;
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public Node(int val) {
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this.val = val;
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this.next = null;
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this.random = null;
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}
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}
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/*
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// Definition for a Node.
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class Node {
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public int val;
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public Node next;
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public Node random;
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public Node() {}
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public Node(int _val,Node _next,Node _random) {
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val = _val;
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next = _next;
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random = _random;
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}
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};
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*/
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public Node copyRandomList(Node head) {
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public ListNode reverseBetween(ListNode head, int left, int right) {
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if (head == null) {
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return null;
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}
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createWeavedList(head);
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linkRandomPointersForNewNodes(head);
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return unweaveList(head);
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}
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ListNode result = new ListNode(0);
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result.next = head;
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// A->B->C --> A->A'->B->B'
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private static void createWeavedList(Node head) {
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for (Node i = head ; i != null ; i = i.next.next) {
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Node newNode = new Node(i.val);
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newNode.next = i.next;
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i.next = newNode;
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ListNode start = result;
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for (int i = 1 ; i < left ; i++) {
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start = start.next;
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}
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}
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private static void linkRandomPointersForNewNodes(Node head) {
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for (Node i = head ; i != null ; i = i.next.next) {
52-
if (i.random == null) {
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continue;
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}
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i.next.random = i.random.next;
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ListNode startNext = start.next, a = startNext, b = start.next.next;
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for (int count = left ; b != null && count < right ; count++) {
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ListNode c = b.next;
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b.next = a;
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a = b;
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b = c;
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}
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start.next = a;
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startNext.next = b;
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return result.next;
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}
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private static Node unweaveList(Node head) {
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final Node pointerNew = head.next;
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for (Node old = head, i = head.next ; i != null && old != null ; i = i.next, old = old.next) {
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old.next = old.next == null ? null : old.next.next;
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i.next = i.next == null ? null : i.next.next;
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}
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return pointerNew;
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public static void main(String[] args) {
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ListNode node = new ListNode(1);
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node.next = new ListNode(2);
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node.next.next = new ListNode(3);
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node.next.next.next = new ListNode(4);
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}
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}

‎src/ListNode.java

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@@ -12,4 +12,11 @@ public class ListNode {
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this.val = val;
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this.next = next;
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}
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@Override
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public String toString() {
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return "ListNode{" +
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"val=" + val +
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'}';
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}
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}

‎src/ReverseNodesInKGroup.java

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// https://leetcode.com/problems/reverse-nodes-in-k-group
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// T: O(N)
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// S: O(1)
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public class ReverseNodesInKGroup {
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public static ListNode reverseKGroup(ListNode head, int k) {
7+
if (head == null || head.next == null || k == 1) {
8+
return head;
9+
}
10+
11+
final ListNode result = new ListNode(0);
12+
result.next = head;
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14+
for (ListNode i = result ; i != null ; ) {
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ListNode start = i;
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17+
// go forward k steps
18+
int count = 0;
19+
for ( ; count < k && i != null ; count++) {
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i = i.next;
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}
22+
23+
if (count == k && i != null) {
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i = reverse(start, i);
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}
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}
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return result.next;
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}
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private static ListNode reverse(ListNode start, ListNode end) {
32+
ListNode a = start.next, b = start.next.next, terminal = end.next;
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a.next = end.next;
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while (b != terminal) {
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ListNode c = b.next;
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b.next = a;
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a = b;
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b = c;
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}
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ListNode newStart = start.next;
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start.next = a;
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return newStart;
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}
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}

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