[Swift]LeetCode41. 缺失的第一个正数 | First Missing Positive

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Given an unsorted integer array, find the smallest missing positive integer.

Example 1:

Input: [1,2,0]
Output: 3

Example 2:

Input: [3,4,-1,1]
Output: 2

Example 3:

Input: [7,8,9,11,12]
Output: 1

Note:

Your algorithm should run in O(n) time and uses constant extra space.

---

 给定一个未排序的整数数组，找出其中没有出现的最小的正整数。

示例 1:

输入: [1,2,0]
输出: 3

示例 2:

输入: [3,4,-1,1]
输出: 2

示例 3:

输入: [7,8,9,11,12]
输出: 1

说明:

你的算法的时间复杂度应为O(n)，并且只能使用常数级别的空间。

---

8ms

class Solution {
    func firstMissingPositive(_ nums: [Int]) -> Int {
        if nums.count == 0 {return 1}
        var nums = nums
        for i in 0..<nums.count {while nums[i] >= 1 && nums[i] <= nums.count && nums[nums[i] - 1] != nums[i] {nums.swapAt(i, nums[i] - 1)}}
        for i in 0..<nums.count {if nums[i] != i + 1 {return i + 1}}
        return nums.count + 1
    }
}

---

12ms

class Solution {
    func firstMissingPositive(_ nums: [Int]) -> Int {
        guard nums.count > 0 else {
            return 1
        }
        var numsCopy = nums
        for  i in 0..<nums.count {
            while numsCopy[i] > 0 && numsCopy[i] < nums.count && numsCopy[numsCopy[i]-1] != numsCopy[i] {
                 numsCopy.swapAt(i, numsCopy[i]-1)
            }
        }
        
        for i in 0..<nums.count {
            if numsCopy[i] != i + 1 {
                return i + 1
            }
        }
        return nums.count + 1
    }
}

---

12ms

class Solution {
    func firstMissingPositive(_ nums: [Int]) -> Int {
    var newNums = nums
    for i in 0..<nums.count {
        while newNums[i] > i + 1 && newNums[i] <= nums.count && newNums[i] != newNums[newNums[i]-1] {
            if newNums[i] <= nums.count && newNums[i] != newNums[newNums[i]-1] {
                let temp = newNums[i]
                newNums[i] = newNums[temp-1]
                newNums[temp-1] = temp
            }
        }
        if newNums[i] > 0 && i + 1 > newNums[i] {
            let temp = newNums[i]
            newNums[i] = newNums[temp-1]
            newNums[temp-1] = temp
        }
    }
    var i = 0
    while i < nums.count {
        if i + 1 != newNums[i] {
            return i + 1
        }
        i = i + 1
    }
    return i + 1
    }
}

---

 16ms

class Solution {
    func firstMissingPositive(_ nums: [Int]) -> Int {
        var set = Set<Int>()
        
        nums.forEach { set.insert($0) }
        
        for i in 0..<nums.count {
            if !set.contains(i + 1) {
                return i + 1
            }
        }
        
        return nums.count + 1
    }
}

---

16ms

class Solution {
    func firstMissingPositive(_ nums: [Int]) -> Int {
        if(nums.count == 0){ return 1 }
        let maximum = nums.max()!
        if(maximum > 0){
            for i in 1...maximum{
                if(!nums.contains(i)){
                    return i
                }
            }
        }
        return maximum + 1
    }
}

---

20ms

class Solution {
    func firstMissingPositive(_ nums: [Int]) -> Int {
        var nums = nums
        nums.append(-1)
        
        if nums.count == 0 {return 1}
        if nums.count == 1 {  return nums[0] == 1 ? 2 : 1 }
        
        for i in 0..<nums.count {
            var val = nums[i]
            while val < nums.count && val >= 0 && nums[val] != val {
                swap(&nums, i, val)
                val = nums[i]
            }
            if val != i  {
                nums[i] = -1
            }
        }
        for i in 1..<nums.count {
            if nums[i] == -1 {
                return i
            }
        }
        return nums.count
    }
    
    func swap(_ nums: inout [Int], _ i: Int, _ j: Int) {
        let temp = nums[i]
        nums[i] = nums[j]
        nums[j] = temp
    }
}

---

32ms

class Solution {
    func firstMissingPositive(_ nums: [Int]) -> Int {
        for i in 1 ..< Int.max {
            if !nums.contains(i) { return i }
        }
        
        return Int.max
    }
}