[Swift]LeetCode414. 第三大的数 | Third Maximum Number
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Given a non-empty array of integers, return the third maximum number in this array. If it does not exist, return the maximum number. The time complexity must be in O(n).
Example 1:
Input: [3, 2, 1] Output: 1 Explanation: The third maximum is 1.
Example 2:
Input: [1, 2] Output: 2 Explanation: The third maximum does not exist, so the maximum (2) is returned instead.
Example 3:
Input: [2, 2, 3, 1] Output: 1 Explanation: Note that the third maximum here means the third maximum distinct number. Both numbers with value 2 are both considered as second maximum.
给定一个非空数组，返回此数组中第三大的数。如果不存在，则返回数组中最大的数。要求算法时间复杂度必须是O(n)。
示例 1:
输入: [3, 2, 1] 输出: 1 解释: 第三大的数是 1.
示例 2:
输入: [1, 2] 输出: 2 解释: 第三大的数不存在, 所以返回最大的数 2 .
示例 3:
输入: [2, 2, 3, 1] 输出: 1 解释: 注意，要求返回第三大的数，是指第三大且唯一出现的数。 存在两个值为2的数，它们都排第二。
12ms:用元组记录数值
1 class Solution { 2 func thirdMax(_ nums: [Int]) -> Int { 3 var (num0,num1,num2) = (Int.min,Int.min,Int.min) 4 for num in nums { 5 if num == num0 || num == num1 || num == num2 { 6 continue 7 } 8 if num > num0 { 9 (num0,num1,num2) = (num,num0,num1) 10 continue 11 } 12 if num > num1 { 13 (num1,num2) = (num,num1) 14 continue 15 } 16 if num > num2 { 17 num2 = num 18 } 19 } 20 return num2 == Int.min ? num0 : num2 21 } 22 }
16ms
1 class Solution { 2 func thirdMax(_ nums: [Int]) -> Int { 3 var firstMax = nums[0] 4 var secondMax: Int? 5 var thirdMax: Int? 6 7 // get max 8 for num in nums { 9 firstMax = max(firstMax, num) 10 } 11 // get 2nd max 12 for num in nums { 13 if num < firstMax { 14 if let curSecondMax = secondMax { 15 secondMax = max(curSecondMax, num) 16 } else { 17 secondMax = num 18 } 19 } 20 } 21 22 if secondMax == nil { 23 return firstMax 24 } 25 26 for num in nums { 27 if num < secondMax! { 28 if let curThirdMax = thirdMax { 29 thirdMax = max(curThirdMax, num) 30 } else { 31 thirdMax = num 32 } 33 } 34 } 35 36 return thirdMax ?? firstMax 37 } 38 }
16ms
1 class Solution { 2 func thirdMax(_ nums: [Int]) -> Int { 3 var firstMax = Int.min 4 var secondMax = Int.min 5 var thirdMax = Int.min 6 var count = 0 7 8 for num in nums { 9 if num > firstMax { 10 (thirdMax, secondMax, firstMax) = (secondMax, firstMax, num) 11 count += 1 12 } else if num != firstMax && num > secondMax { 13 (thirdMax, secondMax) = (secondMax, num) 14 count += 1 15 } else if num != firstMax && num != secondMax && num > thirdMax { 16 thirdMax = num 17 count += 1 18 } 19 } 20 21 if count < 3 { 22 return firstMax 23 } 24 25 return thirdMax 26 } 27 }
20ms
1 class Solution { 2 func thirdMax(_ nums: [Int]) -> Int { 3 var max = nums[0] 4 var second: Int? 5 var third: Int? 6 7 for i in 1..<nums.count { 8 if nums[i] < max { 9 if second == nil { 10 second = nums[i] 11 } else { 12 if second! < nums[i] { 13 third = second! 14 second = nums[i] 15 } else if second! > nums[i] { 16 if third == nil { 17 third = nums[i] 18 } else { 19 if nums[i] > third! { 20 third = nums[i] 21 } 22 } 23 24 } 25 } 26 27 } else if nums[i] > max { 28 third = second 29 second = max 30 max = nums[i] 31 } 32 } 33 34 if third != nil { 35 return third! 36 } 37 38 return max 39 } 40 }
24ms
1 class Solution { 2 func thirdMax(_ nums: [Int]) -> Int { 3 var setNum = Set<Int>(nums) 4 var queue = Queue<Int>(size: 3) 5 6 for num in setNum { 7 if queue.count < 3 { 8 queue.push(value: num) 9 } else if let min = queue.min() { 10 if num > min { 11 queue.pop() 12 queue.push(value: num) 13 } 14 } else { 15 queue.push(value: num) 16 } 17 } 18 19 if queue.count < 3 { 20 while queue.count != 1 { 21 queue.pop() 22 } 23 } 24 25 return queue.min() ?? 0 26 } 27 } 28 29 class Queue<T: Comparable> { 30 private var data = [T]() 31 private let size: Int 32 var count: Int { 33 return data.count 34 } 35 init(size: Int) { 36 self.size = size 37 } 38 39 func push(value: T) { 40 if data.isEmpty { 41 data.append(value) 42 } else if data.count + 1 > size { 43 if let last = data.first { 44 if value < last { 45 data.removeFirst() 46 push(value: value) 47 } 48 } 49 } else { 50 var toInsertAt = -1 51 for (index, dataValue) in data.enumerated() { 52 if value > dataValue { 53 toInsertAt = index 54 break 55 } 56 } 57 if toInsertAt == -1 { 58 data.append(value) 59 } else { 60 data.insert(value, at: toInsertAt) 61 } 62 } 63 } 64 65 @discardableResult 66 func pop() -> T? { 67 return data.popLast() 68 } 69 70 @discardableResult 71 func min() -> T? { 72 if data.isEmpty { 73 return nil 74 } else { 75 return data.last 76 } 77 } 78 }
