[Swift]LeetCode852. 山脈數組的峯頂索引 | Peak Index in a Mountain Array

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➤微信公衆號：山青詠芝（shanqingyongzhi）
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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.

---

咱們把符合下列屬性的數組 A 稱做山脈：

• 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]

給定一個肯定爲山脈的數組，返回任何知足 A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1] 的 i 的值。 

示例 1：

輸入：[0,1,0]
輸出：1

示例 2：

輸入：[0,2,1,0]
輸出：1 

提示：

1. 3 <= A.length <= 10000
2. 0 <= A[i] <= 10^6
3. A 是如上定義的山脈

---

20ms

 1 class Solution {
 2     func peakIndexInMountainArray(_ A: [Int]) -> Int {
 3         var peak = 0
 4         for i in 1..<A.count {
 5             if A[i - 1] < A[i] {
 6                 peak = i
 7             }
 8         }        
 9         return peak
10     }
11 }

---

20ms

 1 class Solution {
 2         func peakIndexInMountainArray(_ A: [Int]) -> Int {
 3         return mountain(0, A.count-1, A)
 4     }
 5 
 6     func mountain(_ from:Int,_ to:Int,_ A: [Int]) -> Int{
 7         if from == to{ return to }
 8         if from == to - 1 { return A[from]>A[to] ? from : to }
 9         let mid = (from + to)/2
10         if A[mid-1] < A[mid] && A[mid] > A[mid+1]{
11             return mid
12         }
13         if A[mid] < A[mid+1] {
14             return mountain(mid,to,A)
15         }else{
16             return mountain(from,mid,A)
17         }
18     }
19 }

---

24ms

 1 class Solution {
 2     func peakIndexInMountainArray(_ A: [Int]) -> Int {
 3         var temp = 0
 4         
 5         for (index, _) in A.enumerated() {
 6             let aValue = A[index]
 7             let bValue = A[index+1]
 8             if aValue > bValue{
 9                 temp = index
10                 break
11             }
12         }
13         return temp
14     }
15 }

---

28ms

 1 class Solution {
 2     func peakIndexInMountainArray(_ A: [Int]) -> Int {
 3         var left = 0, right = A.count - 1
 4     var mid = (left + right) / 2
 5     
 6     while !(A[mid] > A[mid - 1] && A[mid] > A[mid + 1]) {
 7         if (A[mid] < A[mid - 1]) {
 8             right = right - 1
 9         } else {
10             left = left + 1
11         }
12         mid = (left + right) / 2
13     }
14     
15     return mid
16     }
17 }

---

32ms

 1 class Solution {
 2         func peakIndexInMountainArray(_ A: [Int]) -> Int {
 3         return mountain(0, A.count-1, A)
 4     }
 5 
 6     func mountain(_ from:Int,_ to:Int,_ A: [Int]) -> Int{
 7         if to - from < 2 {
 8             if from == to{
 9                 return to
10             }
11             if from == to - 1 {
12                 return A[from]>A[to] ? from : to
13             }
14         }
15         let mid = (from + to)/2
16         if A[mid-1] < A[mid] && A[mid] > A[mid+1]{
17             return mid
18         }
19         if A[mid] < A[mid+1] {
20             return mountain(mid,to,A)
21         }else{
22             return mountain(from,mid,A)
23         }
24     }
25 }

---

84ms

 1 class Solution {
 2     func peakIndexInMountainArray(_ A: [Int]) -> Int {
 3         var right = A.count - 1
 4         var left = 0
 5         while true  {
 6             var middle = (right + left) / 2
 7             let moreThanLast = A[middle] > A[middle - 1]
 8             let moreThanNext =  A[middle] > A[middle + 1]
 9             if moreThanLast && moreThanNext {
10                 return middle
11             }
12             if moreThanLast && !moreThanNext {
13                 left = middle
14             }
15             if !moreThanLast && moreThanNext {
16                 right =  middle
17             }
18         }
19     }
20 }

---

88ms

 1 class Solution {
 2     func peakIndexInMountainArray(_ A: [Int]) -> Int {
 3         for i in 1...A.count-2 {
 4             let ai = A[i]
 5             let ai_1 = A[i-1]
 6             let ai1 = A[i+1]
 7             if ai > ai_1 && ai > ai1 {
 8                 return i;
 9             }
10         }
11         return 0;
12     }
13 }

---

96ms

 1 class Solution {
 2     func peakIndexInMountainArray(_ A: [Int]) -> Int {
 3         for i in 0..<A.count - 1 {
 4             if A[i] > A[i+1] {
 5                 return i
 6             }
 7         }
 8         
 9         return -1
10     }
11 }

---

132 ms

 1 class Solution {
 2     func peakIndexInMountainArray(_ A: [Int]) -> Int {
 3         var result = 0
 4     var climbing = true
 5     if A.count < 3 {
 6         return result
 7     }
 8     for i in 1..<A.count {
 9         if climbing {
10             if A[i-1] < A[i] && A[i] > result {
11                 result = i
12             } else if A[i-1] >= A[i] {
13                 climbing = false
14             }
15         } else {
16             if A[i-1] < A[i] {
17                 result = -1
18             }
19         }
20     }
21     return result
22     }
23 }