[Swift]LeetCode82. 删除排序链表中的重复元素 II | Remove Duplicates from Sorted List II

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Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

Example 1:

Input: 1->2->3->3->4->4->5
Output: 1->2->5

Example 2:

Input: 1->1->1->2->3
Output: 2->3

---

给定一个排序链表，删除所有含有重复数字的节点，只保留原始链表中 没有重复出现 的数字。

示例 1:

输入: 1->2->3->3->4->4->5
输出: 1->2->5

示例 2:

输入: 1->1->1->2->3
输出: 2->3

---

28ms

class Solution {
    func deleteDuplicates(_ head: ListNode?) -> ListNode? {
        var node = head
        var result: ListNode? = nil
        var prevNode: ListNode? = nil
        while node != nil {
            var next = node!.next
            if next != nil && next!.val == node!.val {
                while next != nil && next!.val == node!.val {
                    next = next!.next
                }
                if prevNode != nil {
                    prevNode!.next = next
                } else {
                    if result == nil { result = prevNode }
                }
                node = next
            } else {
                prevNode = node
                if result == nil { result = prevNode }
                node = next
            }
        }
        return result
    }
}

---

32ms

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public var val: Int
 *     public var next: ListNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.next = nil
 *     }
 * }
 */
class Solution {
  func deleteDuplicates(_ head: ListNode?) -> ListNode? {
    let dummyHead = ListNode(0)
    dummyHead.next = head
    var previous: ListNode? = dummyHead
    var current = previous
    
    while current != nil {
      while current?.next != nil && previous?.next?.val == current?.next?.val {
        current = current?.next
      }
      
      if previous?.next === current {
        previous = previous?.next
      } else {
        previous?.next = current?.next
      }
      current = current?.next
    }
    
    return dummyHead.next
  }
}

---

44ms

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public var val: Int
 *     public var next: ListNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.next = nil
 *     }
 * }
 */
class Solution {
    func deleteDuplicates(_ head: ListNode?) -> ListNode? {
        let root = ListNode(-1)
        root.next = head
        var node: ListNode? = root
        while node?.next != nil {
            if node?.next?.val == node?.next?.next?.val {
                let val = node?.next?.val
                while node?.next != nil && node?.next?.val == val {
                    node?.next = node?.next?.next
                }
            } else {
                node = node?.next
            }
        }
        return root.next
    }
}

---

76ms

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public var val: Int
 *     public var next: ListNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.next = nil
 *     }
 * }
 */
class Solution {
    func deleteDuplicates(_ head: ListNode?) -> ListNode? {
        if head == nil {
            return head
        }
        let dummy:ListNode? = ListNode(0)
        dummy?.next = head
        var pre = dummy
        while pre?.next != nil {
            var same = false
            var node = pre?.next
            while node?.next != nil && node!.val == node?.next!.val {
                node = node?.next
                same = true
            }
            if same {
                pre?.next = node?.next
            } else {
                pre = pre?.next
            }
        }
        return dummy?.next
    }
}