[Swift]LeetCode941. 有效的山脈數組 | Valid Mountain Array

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Given an array A of integers, return true if and only if it is a valid mountain array.

Recall that A is a mountain array if and only if:

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

 Example 1:

Input: [2,1]
Output: false 

Example 2:

Input: [3,5,5]
Output: false 

Example 3:

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

 Note:

1. 0 <= A.length <= 10000
2. 0 <= A[i] <= 10000 

---

給定一個整數數組 A，若是它是有效的山脈數組就返回 true，不然返回 false。

讓咱們回顧一下，若是 A 知足下述條件，那麼它是一個山脈數組：

• A.length >= 3
• 在 0 < i < A.length - 1 條件下，存在 i 使得：
  • A[0] < A[1] < ... A[i-1] < A[i]
  • A[i] > A[i+1] > ... > A[B.length - 1]

示例 1：

輸入：[2,1]
輸出：false

示例 2：

輸入：[3,5,5]
輸出：false

示例 3：

輸入：[0,3,2,1]
輸出：true

 提示：

1. 0 <= A.length <= 10000
2. 0 <= A[i] <= 10000 

---

256ms

 1 class Solution {
 2     func validMountainArray(_ A: [Int]) -> Bool {
 3         var n:Int = A.count
 4         if n < 3 {return false}
 5         var pre:Int = n - 1
 6         for i in 0..<(n - 1)
 7         {
 8             if A[i] >= A[i + 1]
 9             {
10                 pre = i
11                 break
12             }
13         }
14         if pre == 0 || pre == n-1 {return false}
15         for i in pre..<(n - 1)
16         {
17             if A[i] <= A[i + 1] {return false}
18         }
19         return true
20     }
21 }

---

256ms

 1 class Solution {
 2     func validMountainArray(_ A: [Int]) -> Bool {
 3         let n = A.count
 4         var i = 0
 5         var j = n-1
 6         while i + 1 < n , A[i] < A[i+1]{
 7             i+=1
 8         }
 9         while j > 0 , A[j] < A[j-1]{
10             j-=1
11         }
12         
13         return i == j && i > 0 && i < n - 1
14     }
15 }

---

260ms

 1 class Solution {
 2     func validMountainArray(_ A: [Int]) -> Bool {
 3         var i = 1
 4         while i < A.count && A[i] > A[i-1] {
 5             i += 1
 6         }
 7         if i == 1 || i == A.count { return false }
 8         while i < A.count && A[i] < A[i-1] {
 9             i += 1
10         }
11         return i == A.count
12     }
13 }

---

264ms

 1 class Solution {
 2     func validMountainArray(_ A: [Int]) -> Bool {
 3         if A.count < 3 {
 4             return false
 5         }
 6         
 7         if A[0] > A[1] {
 8             return false
 9         }
10         
11         var startedFalling = false
12         for i in 1..<A.count {
13             if A[i-1] < A[i] {
14                 if startedFalling {
15                     return false
16                 }
17             } else if A[i-1] > A[i] {
18                 startedFalling = true
19             } else {
20                 return false
21             }
22         }
23         
24         return startedFalling
25     }
26 }

---

388ms

 1 class Solution {
 2     func validMountainArray(_ A: [Int]) -> Bool {
 3         if A.count == 0 {
 4             return false
 5         }
 6         
 7         var maxValue = A.max()!
 8         var result = true
 9         var direction = 0
10         // 0 -> increase ; 1 -> decrease
11         
12         if A[0] == maxValue {
13             return false
14         }
15         
16         for index in 0..<A.count-1 {
17             if A[index] == maxValue {direction = 1}
18             
19             if (direction == 0 && A[index] >= A[index+1]) ||
20             (direction == 1 && A[index] <= A[index+1])
21             {
22                 result = false
23                 break
24             }
25         }
26         
27         if direction == 0 {
28             return false
29         }
30         
31         return result
32     }
33 }