LC#25 Reverse nodes in LinkedList in group of K, two approaches

Author: NirmalSilwal

Leetcode/leetcodeTags/LinkedList/ReverseNodesInK_Group25.java

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+package LinkedList;
+
+public class ReverseNodesInK_Group25 {
+
+	public class ListNode {
+		int val;
+		ListNode next;
+
+		ListNode() {
+		}
+
+		ListNode(int val) {
+			this.val = val;
+		}
+
+		ListNode(int val, ListNode next) {
+			this.val = val;
+			this.next = next;
+		}
+	}
+
+	// time: O(n), space: O(n/k)
+	public ListNode reverseKGroup(ListNode head, int k) {
+		if (head == null || head.next == null || k == 1)
+			return head;
+
+		ListNode start = head;
+		ListNode end = head;
+		int moveEndCursor = k - 1;
+
+		while (moveEndCursor != 0) {
+			end = end.next;
+			moveEndCursor--;
+
+			if (end == null)
+				return head;
+		}
+
+		ListNode newHead = reverseKGroup(end.next, k);
+
+		reverseIterative(start, end);
+
+		start.next = newHead;
+
+		return end;
+	}
+
+	private void reverseIterative(ListNode start, ListNode end) {
+
+		ListNode prev = null;
+		ListNode curr = start;
+		ListNode nxt = start.next;
+
+		while (prev != end) {
+			curr.next = prev;
+			prev = curr;
+			curr = nxt;
+
+			if (nxt != null)
+				nxt = nxt.next;
+		}
+	}
+
+	// 2nd approach
+	public ListNode reverseKGroupSpaceEfficient(ListNode head, int k) {
+		f
+	}
+
+}