LeetCode-896.Monotonic Array 单调数组（C++实现）

一、问题描述
An array is monotonic if it is either monotone increasing or monotone decreasing.
An array A is monotone increasing if for all i <= j, A[i] <= A[j]. An array A is monotone decreasing if for all i <= j, A[i] >= A[j].
Return true if and only if the given array A is monotonic.

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

Example 2:
Input: [6,5,4,4]
Output: true

Example 3:
Input: [1,3,2]
Output: false

Example 4:
Input: [1,2,4,5]
Output: true

Example 5:
Input: [1,1,1]
Output: true

Note:
1）1 <= A.length <= 50000
2）-100000 <= A[i] <= 100000
要求：判断数组A是否为单调数组，即对所有的 i <= j, A[i] <= A[j]，或者对所有的 i <= j, A[i] >= A[j]。若为单调数组，返回true，否则返回false。
二、思路及代码
思路：
刚开始我想的是，遍历数组A，当其为升序或者降序时࿰