LeetCode 896. Monotonic Array

题目描述：

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:

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

Example 2:

1 2	Input: [6,5,4,4] Output: true

Example 3:

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

Example 4:

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

Example 5:

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

Note:

1 2	1 <= A.length <= 50000 -100000 <= A[i] <= 100000

题目大意：

一个单调数组的定义就是数组元素单调递增或者单调递减。
测试样例见题目描述

解题思路：

对于n个元素数组来说判断是否递增/减的方法就是遍历一遍数组元素看看是递增还是递减。
A[i] >= A[i - 1]; // 递增 A[i] <= A[i - 1]; // 递减

参考LeetCode Discuss：
https://leetcode.com/problems/monotonic-array/discuss/165899/1-liner-C++

C++代码：

class Solution {
public:
    bool isMonotonic(vector<int>& A) {
        int size = A.size();
        if ( A[size - 1] > A[0]) {
            for (int i = 0; i < size - 1; ++i) {
                if (A[i + 1] - A[i] < 0) return false;
            }
            return true;
        }
        else {
            for (int i = 0; i < size - 1; ++i) {
                if (A[i] - A[i + 1] < 0) return false;
            }
            return true;
        }
    }
};