[Swift]LeetCode628. 三个数的最大乘积 | Maximum Product of Three Numbers

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★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★Given an integer array, find three numbers whose product is maximum and output the maximum product.

Example 1:

Input: [1,2,3]
Output: 6 

Example 2:

Input: [1,2,3,4]
Output: 24 

Note:

1. The length of the given array will be in range [3,104] and all elements are in the range [-1000, 1000].
2. Multiplication of any three numbers in the input won't exceed the range of 32-bit signed integer.

---

给定一个整型数组，在数组中找出由三个数组成的最大乘积，并输出这个乘积。

示例 1:

输入: [1,2,3]
输出: 6

示例 2:

输入: [1,2,3,4]
输出: 24

注意:

1. 给定的整型数组长度范围是[3,104]，数组中所有的元素范围是[-1000, 1000]。
2. 输入的数组中任意三个数的乘积不会超出32位有符号整数的范围。

---

136ms

class Solution {
    func maximumProduct(_ nums: [Int]) -> Int {
        if(nums.count == 3){ return nums[0] * nums[1] * nums[2] }
        let sorted = nums.sorted(by: >)
        if(sorted[sorted.count - 1] >= 0 || sorted[0] < 0){
            return sorted[0] * sorted[1] * sorted[2]
        }
        //只有一个负数的情况,取三个正数
        if(sorted[sorted.count - 1] < 0 && sorted[sorted.count - 2] > 0){
            return sorted[0] * sorted[1] * sorted[2]
        }
        //有多个负数情况，比较
        let neg = sorted[sorted.count - 2] * sorted[sorted.count - 1]
        let pos = sorted[1] * sorted[2]
        return sorted[0] * max(neg, pos)
    }
}

---

180ms

class Solution {
    func maximumProduct(_ nums: [Int]) -> Int {
        var nums = nums
        nums.sort { $0 > $1 }
        
        let count = nums.count
        return max(nums[0] * nums[1] * nums[2],
                   nums[0] * nums[count - 1] * nums[count - 2])
    }
}

---

252ms

class Solution {
    func maximumProduct(_ nums: [Int]) -> Int {
    if nums.count < 3 {
        return 0
    }
    var numsTemp : [Int] = nums.sorted()
    if numsTemp[1] > 0 {
        return numsTemp.last! * numsTemp[numsTemp.count - 2] * numsTemp[numsTemp.count - 3]
    } else {
        if numsTemp.last! <= 0 {
            return numsTemp.last! * numsTemp[numsTemp.count - 2] * numsTemp[numsTemp.count - 3]
        } else {
            return numsTemp.last! * numsTemp[numsTemp.count - 2] * numsTemp[numsTemp.count - 3] > numsTemp.first! * numsTemp[1] * numsTemp.last! ? numsTemp.last! * numsTemp[numsTemp.count - 2] * numsTemp[numsTemp.count - 3] : numsTemp.first! * numsTemp[1] * numsTemp.last!
        }
     }
   }
}

---

Runtime: 272 ms

Memory Usage: 19 MB

class Solution {
    func maximumProduct(_ nums: [Int]) -> Int {
        var mx1:Int = Int.min
        var mx2:Int = Int.min
        var mx3:Int = Int.min
        var mn1:Int = Int.max
        var mn2:Int = Int.max
        for num in nums
        {
            if num > mx1
            {
                mx3 = mx2
                mx2 = mx1
                mx1 = num
            }
            else if num > mx2
            {
                mx3 = mx2
                mx2 = num
            }
            else if num > mx3
            {
                mx3 = num
            }
            if num < mn1
            {
                mn2 = mn1
                mn1 = num
            }
            else if num < mn2
            {
                mn2 = num
            }            
        }
        return max(mx1 * mx2 * mx3, mx1 * mn1 * mn2)
    }
}

---

320ms

class Solution {
    func maximumProduct(_ nums: [Int]) -> Int {
        if nums.count < 3 { return Int.min }
        var max1 = Int.min
        var max2 = max1
        var max3 = max1
        var min1 = Int.max
        var min2 = Int.max
        
        nums.forEach {
            if $0 >= max1 {
                max3 = max2
                max2 = max1
                max1 = $0
            } else if $0 >= max2 {
                max3 = max2
                max2 = $0
            } else if $0 > max3 {
                max3 = $0
            }
            
            if $0 <= min1 {
                min2 = min1
                min1 = $0
            } else if $0 <= min2 {
                min2 = $0
            }
        }
            let val1 = max1 * max2 * max3
            let val2 = min1 * min2 * max1
        
            return max(val1, val2)
    }   
}

---

388ms

class Solution {
    func maximumProduct(_ nums: [Int]) -> Int {
        
        let sorted = nums.sorted()
        
        if sorted[sorted.count - 1] == 0 {
            return 0
        } else if sorted[sorted.count - 1] < 0 {
            return sorted[0] * sorted[1] * sorted[sorted.count - 1]
        } else if sorted[0] >= 0 {
            return sorted[sorted.count - 1] * sorted[sorted.count - 2] * sorted[sorted.count - 3]
        } else {
            return max(sorted[sorted.count - 1] * sorted[sorted.count - 2] * sorted[sorted.count - 3],
                      sorted[0] * sorted[1] * sorted[sorted.count - 1])
        }
    }
}

---

392ms

class Solution {
    func maximumProduct(_ nums: [Int]) -> Int {
        let sorted = nums.sorted()
        return max(sorted[nums.count - 1] * sorted[nums.count - 2] * sorted[nums.count - 3], sorted[nums.count - 1] * sorted[0] * sorted[1])
    }
}

---

404ms

class Solution {
    func maximumProduct(_ nums: [Int]) -> Int {
        if nums.count == 3 {
            return nums.reduce(1, *)
        }
        var sort = nums.sorted(by: >)
        let one = sort[0] * sort[1] * sort[2]
        let two = sort[0] * sort[nums.count - 1] * sort[nums.count - 2]
        
        return max(one, two)
    }
}

---

440ms

class Solution {
    func maximumProduct(_ nums: [Int]) -> Int {
        let sortGreatestToLeast: [Int] = nums.sorted(by: >)
        let greatestThreeNums: [Int] = Array(sortGreatestToLeast.prefix(3))
        let leastTwoNums: [Int] = Array(sortGreatestToLeast.suffix(2))
        let productFromGreatest: Int = greatestThreeNums.reduce(1, { x, y in x * y })
        let productFromBoth: Int = leastTwoNums.reduce(1, { x, y in x * y }) * greatestThreeNums.first!
        return productFromGreatest > productFromBoth ? productFromGreatest : productFromBoth
    }
}