Recognize Nondecreasing or Nonincreasing Arrays
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
### Problem
Return whether `nums` is monotonic: either every earlier value is no greater than every later value, or every earlier value is no smaller than every later value. Equal adjacent values are allowed in either direction.
```cpp
class Solution {
public:
bool isMonotonic(vector<int>& nums);
};
```
### Examples
**Example 1:**
```text
Input: nums = [4,4,2,-1]
Output: true
Explanation: Every step is nonincreasing, including the initial equality.
```
**Example 2:**
```text
Input: nums = [2,2,5,3]
Output: false
Explanation: The rise2 to5 rules out nonincreasing order, while the fall5 to3 rules out nondecreasing order.
```
### Constraints
- `1 <= nums.length <= 10^5`.
- `-10^5 <= nums[i] <= 10^5`.
### Contract considerations
This is weak monotonicity; equal values do not break either direction.
```hint Read the boundary condition
Which adjacent comparisons disprove each of the two possible directions?
```
### Boundary reminders
This is weak monotonicity; equal values do not break either direction.
Overview: Recognize Nondecreasing or Nonincreasing Arrays. Return whether nums is monotonic: either every earlier value is no greater than every later value, or every earlier value is no smaller than every later value.