Monotonic Array

Description

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

Solution(javascript)

/**
 * @param {number[]} A
 * @return {boolean}
 */
const isMonotonic = function (A) {
  let increasing = true
  let decreasing = true
  for (let i = 0; i < A.length; i++) {
    if (A[i] > A[i + 1]) {
      increasing = false
    }
    if (A[i] < A[i + 1]) {
      decreasing = false
    }
  }
  return increasing || decreasing
}