[Swift]LeetCode456. 132模式 | 132 Pattern

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Given a sequence of n integers a1, a2, ..., an, a 132 pattern is a subsequence ai, aj, ak such that i < j < k and ai < ak < aj. Design an algorithm that takes a list of n numbers as input and checks whether there is a 132 pattern in the list.

Note: n will be less than 15,000.

Example 1:

Input: [1, 2, 3, 4]

Output: False

Explanation: There is no 132 pattern in the sequence. 

Example 2:

Input: [3, 1, 4, 2]

Output: True

Explanation: There is a 132 pattern in the sequence: [1, 4, 2]. 

Example 3:

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

Output: True

Explanation: There are three 132 patterns in the sequence: [-1, 3, 2], [-1, 3, 0] and [-1, 2, 0].

---

给定一个整数序列：a1, a2, ..., an，一个132模式的子序列 ai, aj, ak 被定义为：当 i < j < k时，ai < ak < aj。设计一个算法，当给定有 n 个数字的序列时，验证这个序列中是否含有132模式的子序列。

注意：n 的值小于15000。

示例1:

输入: [1, 2, 3, 4]

输出: False

解释: 序列中不存在132模式的子序列。

示例 2:

输入: [3, 1, 4, 2]

输出: True

解释: 序列中有 1 个132模式的子序列： [1, 4, 2].

示例 3:

输入: [-1, 3, 2, 0]

输出: True

解释: 序列中有 3 个132模式的的子序列: [-1, 3, 2], [-1, 3, 0] 和 [-1, 2, 0].

---

164ms

struct Stack<T> {
    var items = [T]()
    mutating func push(item: T) {
        items.append(item)
    }
    mutating func pop() -> T {
        return items.removeLast()
    }
    func top() -> T {
        return items.last!
    }
    func empty() -> Bool {
        return items.count == 0
    }
}

class Solution {
    func find132pattern(_ nums: [Int]) -> Bool {
        var third = Int.min
        var s = Stack<Int>()
        for i in stride(from: nums.count - 1, through: 0, by: -1) {
            if nums[i] < third {
                return true
            }else {
                while !s.empty() && (nums[i] > s.top()) {
                    third = s.top()
                    _ = s.pop()
                }
                s.push(item: nums[i])
            }
        }
        return false
    }
}

---

324ms

class Solution {
    func find132pattern(_ nums: [Int]) -> Bool {
        var hanoi = Array<Int>.init();
        var medNum = Int.min
        for index in stride(from: nums.count-1, through: 0, by: -1) {
            if nums[index] < medNum {
                return true
            } else {
                while (hanoi.count > 0 && hanoi.last! < nums[index]) {
                    medNum = hanoi.last!
                    hanoi.removeLast()
                }
            }
            hanoi.append(nums[index])
        }
        return false
    }
}

---

1348ms

class Solution {
    func find132pattern(_ nums: [Int]) -> Bool {
        if nums.count < 3{ 
            return false 
        }
        var newNums = [nums[0]]
        for i in 1..<nums.count {
            if nums[i] != nums[i-1]{
                newNums.append(nums[i]);
            }
        }
        if newNums.count < 3{ 
            return false 
        }
        var minArr = [newNums[0]]
        var min = newNums[0]
        for i in newNums{
            if i < min{
                min = i
            }
            minArr.append(min)
        }
        for i in 1..<newNums.count-1{
            let a = minArr[i]
            let b = newNums[i]
            if a >= b{ 
                continue 
            }
            for j in (i+1)..<newNums.count{
                let c = newNums[j]
                if c > a && c < b {
                    return true
                }
            }
        }
        return false
    }
}

---

4388ms

class Solution {
    func find132pattern(_ nums: [Int]) -> Bool {
        if nums.count < 3 {
            return false
        }
        var i = nums.count
        var min = nums[i - 1]
        while (i > 0) {
            min = nums[i - 1]
            var j = nums.count
            var max = min
            while (j > i) {
                let t = nums[j - 1]
                if t > min {
                    if max > min {
                        if t > max {
                            return true
                        }else {
                            max = t
                        }
                    }else {
                        max = t
                    }
                }
                j = j - 1
            }
            i = i - 1
        }
        return false
    }
}

---

6656ms

class Solution {
    func find132pattern(_ nums: [Int]) -> Bool {
        var n:Int = nums.count
        var i:Int = 0
        var j:Int = 0
        var k:Int = 0
        while (i < n) {
            while (i < n - 1 && nums[i] >= nums[i + 1])
            {
                i += 1
            }
            j = i + 1;
            while (j < n - 1 && nums[j] <= nums[j + 1])
            {
                 j += 1
            }
            k = j + 1
            while (k < n) {
                if nums[k] > nums[i] && nums[k] < nums[j]
                {
                     return true
                }
                k += 1
            }
            i = j + 1
        }
        return false
    }
}