Formatted question description: https://leetcode.ca/all/896.html

896. Monotonic Array (Easy)

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

Companies:
Facebook

Related Topics:
Array

Solution 1.

// OJ: https://leetcode.com/problems/monotonic-array/

// 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;
    }
};

Java

class Solution {
    public boolean isMonotonic(int[] A) {
        int length = A.length;
        if (length <= 2)
            return true;
        int prevDifference = 0;
        for (int i = 1; i < length; i++) {
            int difference = A[i] - A[i - 1];
            if (prevDifference > 0 && difference < 0 || prevDifference < 0 && difference > 0)
                return false;
            if (difference != 0)
                prevDifference = difference;
        }
        return true;
    }
}

All Problems

All Solutions