896

896. Monotonic Array (Easy)

An array is monotonic if it is either monotone increasing or monotone decreasing.

An array nums is monotone increasing if for all i <= j, nums[i] <= nums[j]. An array nums is monotone decreasing if for all i <= j, nums[i] >= nums[j].

Given an integer array nums, return true if the given array is monotonic, or false otherwise.

 

Example 1:

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

Example 2:

Input: nums = [6,5,4,4]
Output: true

Example 3:

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

 

Constraints:

• 1 <= nums.length <= 105
• -105 <= nums[i] <= 105

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Related Topics:
Array

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Solution 1.

// OJ: https://leetcode.com/problems/monotonic-array/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    bool isMonotonic(vector<int>& A) {
        int dir = 0;
        for (int i = 1; i < A.size(); ++i) {
            int d = A[i] == A[i - 1] ? 0 : (A[i] > A[i - 1] ? 1 : -1);
            if (dir && d && dir != d) return false;
            if (d) dir = d;
        }
        return true;
    }
};