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，如果它是有效的山脈數組就返回 true，否則返回 false。

讓我們回顧一下，如果 A 滿足下述條件，那麽它是一個山脈數組：

• 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

456ms

 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 }

[Swift Weekly Contest 111]LeetCode941. 有效的山脈數組 | Valid Mountain Array