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Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

Your algorithm should run in O(n) complexity.

Example:

Input: [100, 4, 200, 1, 3, 2]Output: 4Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.

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给定一个未排序的整数数组，找出最长连续序列的长度。

要求算法的时间复杂度为 O(n)。

示例:

输入: [100, 4, 200, 1, 3, 2]输出: 4解释: 最长连续序列是 [1, 2, 3, 4]。它的长度为 4。

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16ms

1 class Solution { 2     func longestConsecutive(_ nums: [Int]) -> Int { 3         guard nums.count > 0 else { return 0 } 4         var nums = nums.sorted(){$0 < $1} 5          6         var longestStreak = 1 7         var currentStreak = 1 8         for i in 1..

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20ms

1 class Solution { 2     func longestConsecutive(_ nums: [Int]) -> Int { 3         let set = Set(nums) 4          5         var longestStreak = 0 6          7         for s in set { 8             if !set.contains(s - 1) { 9                 var currentNumber = s10                 var currentStreak = 111                 12                 while set.contains(currentNumber + 1) {13                     currentNumber += 114                     currentStreak += 115                 }16                 17                 longestStreak = max(longestStreak, currentStreak)18             }19         }20         21         return longestStreak22     }23 }

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24ms

1 class Solution { 2     func longestConsecutive(_ nums: [Int]) -> Int { 3         var numSet = Set(nums) 4         var longest = 0 5         for num in nums { 6             if numSet.contains(num) { 7                 var left = num - 1 8                 var right = num + 1 9                 numSet.remove(num)10                 while numSet.contains(left) {11                     numSet.remove(left)12                     left -= 113                 }14                 while numSet.contains(right) {15                     numSet.remove(right)16                     right += 117                 }18                 longest = max(longest, right - left - 1)19             }20         }21         return longest22     }23 }

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36ms

1 class Solution { 2     func longestConsecutive(_ nums: [Int]) -> Int { 3         var set = Set(nums), longest = 0 4          5         for num in nums { 6             if set.contains(num) { 7                 set.remove(num) 8                 let distance = 1 + findConsecutive(&set, num, 1) + findConsecutive(&set, num, -1) 9                 longest = max(longest, distance)10             }11         }12         13         return longest14     }15     16     fileprivate func findConsecutive(_ set: inout Set
     
      , _ num: Int, _ step: Int) -> Int {17         var len = 0, num = num + step18     19         while set.contains(num) {20             set.remove(num)21             len += 122             num += step23         }24         25         return len26     }27 }
     

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 48ms

1 class Solution { 2     func longestConsecutive(_ nums: [Int]) -> Int { 3         guard nums.count > 1 else { 4             return nums.count 5         } 6  7         let sorted = nums.sorted() 8         var last = 0 9         var maxLength = 110         var duplicated = 011 12         for idx in 1 ..< sorted.count {13             if sorted[idx] == sorted[idx - 1] {14                 duplicated += 115             } else if sorted[idx] == sorted[idx - 1] + 1 {16                 let length = idx - duplicated - last + 117                 maxLength = max(maxLength, length)18             } else {19                 duplicated = 020                 last = idx21             }22         }23 24         return maxLength25     }26 }

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56ms

1 public struct HashSet
     
       { 2   private var dictionary = Dictionary
      
       () 3      4   public mutating func insert(element: T) { 5     dictionary[element] = true 6   } 7   public mutating func remove(element: T) { 8     dictionary[element] = nil 9   }10   public func contains(element: T) -> Bool {11     return dictionary[element] != nil12   }13   public func allElements() -> [T] {14     return Array(dictionary.keys)15   }16   public var count: Int {17     return dictionary.count18   }19   public var isEmpty: Bool {20     return dictionary.isEmpty21   }22 }23 24 /*25  * Copyright (c) 2018 Brad McEvilly26  */27 class Solution {28     func longestConsecutive(_ nums: [Int]) -> Int {29         30         var maxStreak:Int=031         var numSet = HashSet
       
        ()32         33         // validate input34         if (0 == nums.count || nums==nil){35             //print("validation for nums - nums:\(nums)")36             return maxStreak37         }38         39         for i in (0..