[Swift]LeetCode852. 山脉数组的峰顶索引 | Peak Index in a Mountain Array

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Let's call an array A a mountain if the following properties hold:

• A.length >= 3
• There exists some 0 < i < A.length - 1 such that A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1]

Given an array that is definitely a mountain, return any i such that A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1].

Example 1:

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

Example 2:

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

Note:

1. 3 <= A.length <= 10000
2. 0 <= A[i] <= 10^6
3. A is a mountain, as defined above.

---

我们把符合下列属性的数组 A 称作山脉：

• A.length >= 3
• 存在 0 < i < A.length - 1 使得A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1]

给定一个确定为山脉的数组，返回任何满足 A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1] 的 i 的值。 

示例 1：

输入：[0,1,0]
输出：1

示例 2：

输入：[0,2,1,0]
输出：1 

提示：

1. 3 <= A.length <= 10000
2. 0 <= A[i] <= 10^6
3. A 是如上定义的山脉

---

20ms

class Solution {
    func peakIndexInMountainArray(_ A: [Int]) -> Int {
        var peak = 0
        for i in 1..<A.count {
            if A[i - 1] < A[i] {
                peak = i
            }
        }        
        return peak
    }
}

---

20ms

class Solution {
        func peakIndexInMountainArray(_ A: [Int]) -> Int {
        return mountain(0, A.count-1, A)
    }

    func mountain(_ from:Int,_ to:Int,_ A: [Int]) -> Int{
        if from == to{ return to }
        if from == to - 1 { return A[from]>A[to] ? from : to }
        let mid = (from + to)/2
        if A[mid-1] < A[mid] && A[mid] > A[mid+1]{
            return mid
        }
        if A[mid] < A[mid+1] {
            return mountain(mid,to,A)
        }else{
            return mountain(from,mid,A)
        }
    }
}

---

24ms

class Solution {
    func peakIndexInMountainArray(_ A: [Int]) -> Int {
        var temp = 0
        
        for (index, _) in A.enumerated() {
            let aValue = A[index]
            let bValue = A[index+1]
            if aValue > bValue{
                temp = index
                break
            }
        }
        return temp
    }
}

---

28ms

class Solution {
    func peakIndexInMountainArray(_ A: [Int]) -> Int {
        var left = 0, right = A.count - 1
    var mid = (left + right) / 2
    
    while !(A[mid] > A[mid - 1] && A[mid] > A[mid + 1]) {
        if (A[mid] < A[mid - 1]) {
            right = right - 1
        } else {
            left = left + 1
        }
        mid = (left + right) / 2
    }
    
    return mid
    }
}

---

32ms

class Solution {
        func peakIndexInMountainArray(_ A: [Int]) -> Int {
        return mountain(0, A.count-1, A)
    }

    func mountain(_ from:Int,_ to:Int,_ A: [Int]) -> Int{
        if to - from < 2 {
            if from == to{
                return to
            }
            if from == to - 1 {
                return A[from]>A[to] ? from : to
            }
        }
        let mid = (from + to)/2
        if A[mid-1] < A[mid] && A[mid] > A[mid+1]{
            return mid
        }
        if A[mid] < A[mid+1] {
            return mountain(mid,to,A)
        }else{
            return mountain(from,mid,A)
        }
    }
}

---

84ms

class Solution {
    func peakIndexInMountainArray(_ A: [Int]) -> Int {
        var right = A.count - 1
        var left = 0
        while true  {
            var middle = (right + left) / 2
            let moreThanLast = A[middle] > A[middle - 1]
            let moreThanNext =  A[middle] > A[middle + 1]
            if moreThanLast && moreThanNext {
                return middle
            }
            if moreThanLast && !moreThanNext {
                left = middle
            }
            if !moreThanLast && moreThanNext {
                right =  middle
            }
        }
    }
}

---

88ms

class Solution {
    func peakIndexInMountainArray(_ A: [Int]) -> Int {
        for i in 1...A.count-2 {
            let ai = A[i]
            let ai_1 = A[i-1]
            let ai1 = A[i+1]
            if ai > ai_1 && ai > ai1 {
                return i;
            }
        }
        return 0;
    }
}

---

96ms

class Solution {
    func peakIndexInMountainArray(_ A: [Int]) -> Int {
        for i in 0..<A.count - 1 {
            if A[i] > A[i+1] {
                return i
            }
        }
        
        return -1
    }
}

---

132 ms

class Solution {
    func peakIndexInMountainArray(_ A: [Int]) -> Int {
        var result = 0
    var climbing = true
    if A.count < 3 {
        return result
    }
    for i in 1..<A.count {
        if climbing {
            if A[i-1] < A[i] && A[i] > result {
                result = i
            } else if A[i-1] >= A[i] {
                climbing = false
            }
        } else {
            if A[i-1] < A[i] {
                result = -1
            }
        }
    }
    return result
    }
}