rewrite

Author: mengli

RemoveDuplicatesfromSortedListII.java

@@ -1,40 +1,32 @@
-
-
-/** 
- * Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.
- *
- * For example,
- * Given 1->2->3->3->4->4->5, return 1->2->5.
- * Given 1->1->1->2->3, return 2->3.
+/**
+ * Given a sorted linked list, delete all nodes that have duplicate numbers,
+ * leaving only distinct numbers from the original list.
+ * 
+ * For example, Given 1->2->3->3->4->4->5, return 1->2->5. Given 1->1->1->2->3,
+ * return 2->3.
  */
 
 public class RemoveDuplicatesfromSortedListII {
 	public ListNode deleteDuplicates(ListNode head) {
-		ListNode begin = head;
-		ListNode cur = head;
-		ListNode newHead = null;
-		ListNode newTail = null;
-		while (cur != null) {
-			while (cur.next != null && begin.val == cur.next.val) {
-				cur = cur.next;
-			}
-			if (begin != cur) {
-				begin = cur.next;
-				cur = cur.next;
-			} else {
-				ListNode tmp = begin;
-				begin = begin.next;
-				cur = cur.next;
-				if (newHead == null) {
-					newHead = tmp;
-					newTail = tmp;
+		if (head == null)
+			return head;
+		ListNode start = new ListNode(0);
+		start.next = head;
+		ListNode slow = start;
+		ListNode fast = head;
+		while (fast.next != null) {
+			if (slow.next.val != fast.next.val) {
+				if (slow.next.next == fast.next) {
+					slow = slow.next;
 				} else {
-					newTail.next = tmp;
-					newTail = newTail.next;
+					slow.next = fast.next;
 				}
-				newTail.next = null;
 			}
+			fast = fast.next;
+		}
+		if (slow.next.next != fast.next) {
+			slow.next = fast.next;
 		}
-		return newHead;
+		return start.next;
 	}
 }

ReverseLinkedListII.java

@@ -1,5 +1,3 @@
-
-
 /** 
  * Reverse a linked list from position m to n. Do it in-place and in one-pass.
  * 
@@ -12,32 +10,40 @@
 
 public class ReverseLinkedListII {
 	public ListNode reverseBetween(ListNode head, int m, int n) {
-		if (head == null)
-			return head;
-		int start = 1, end = 0;
-		ListNode s = head;
-		ListNode p = null;
-		while (start++ < m && s != null) {
-			p = s;
-			s = s.next;
+		ListNode start = new ListNode(0);
+		start.next = head;
+		ListNode low = start;
+		ListNode high = start;
+		ListNode p1 = null;
+		ListNode p2 = null;
+		for (int i = 0; i < m - 1; i++) {
+			low = low.next;
 		}
-		ListNode cur = null;
-		ListNode next = null;
+		p1 = low;
+		low = low.next;
+		for (int i = 0; i < n; i++) {
+			high = high.next;
+		}
+		p2 = high.next;
+		high.next = null;
+		p1.next = reverseList(low);
+		while (p1.next != null) {
+			p1 = p1.next;
+		}
+		p1.next = p2;
+		return start.next;
+	}
+
+	private ListNode reverseList(ListNode low) {
+		ListNode cur = low;
 		ListNode prev = null;
-		end = m;
-		cur = s;
-		while (end++ <= n && cur != null) {
+		ListNode next = null;
+		while (cur != null) {
 			next = cur.next;
 			cur.next = prev;
 			prev = cur;
 			cur = next;
 		}
-		s.next = cur;
-		if (p != null) {
-			p.next = prev;
-			return head;
-		} else {
-			return prev;
-		}
+		return prev;
 	}
 }