LeetCode 896. Monotonic Array

题目

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.

题意

检查阵列是否为递增或递减阵列，可接受相同元素，若阵列中同时出现递增与递减情况，即无法通过验证。

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

Example 4:

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

Example 5:

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

解题想法

宣告变数，up、down，若出现递增，则down = 0，出现递减up = 0，如果最终down = 0与up = 0，表示无法通过验证。

Solution

var isMonotonic = function (A) {
  let up = 1;
  let down = 1;
  for (let i = 1; i < A.length; i++) {
    if (A[i] > A[i - 1]) {
      down = 0;
    } else if (A[i] < A[i - 1]) {
      up = 0;
    }
  };
  return (down || up);
};