a

Author: anishLearnsToCode

src/ReverseLinkedListII.java

@@ -0,0 +1,46 @@
+public class ReverseLinkedListII {
+    private static class ListNode {
+        int val;
+        ListNode next;
+        ListNode(int val) { this.val = val; }
+    }
+
+    public ListNode reverseBetween(ListNode head, int leftVal, int rightVal) {
+        if (leftVal == rightVal) return head;
+
+        ListNode sentinelHead = new ListNode(-1000);
+        sentinelHead.next = head;
+        ListNode beforeLeft = getNodeBefore(sentinelHead, leftVal);
+        System.out.println(beforeLeft.val);
+        ListNode left = beforeLeft.next;
+//        ListNode afterRight = getNodeAfter(sentinelHead, rightVal);
+        ListNode a = beforeLeft.next, b = a.next, c = b.next;
+
+        while (c != null && b.val != rightVal) {
+            a.next = null;
+            b.next = a;
+            a = b;
+            b = c;
+            c = c.next;
+        }
+        a.next = null;
+        b.next = a;
+        beforeLeft.next = b;
+        left.next = c;
+        return sentinelHead.next;
+    }
+
+    private ListNode getNodeBefore(ListNode head, int value) {
+        while (head != null && head.next != null && head.next.val != value) {
+            head = head.next;
+        }
+        return head;
+    }
+
+    private ListNode getNodeAfter(ListNode head, int value) {
+        while (head != null && head.val != value) {
+            head = head.next;
+        }
+        return head.next;
+    }
+}