# # 896 Monotonic Array

[LeetCode](https://leetcode.com/problems/monotonic-array/)

```
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.

input: 數字陣列
output: 看是不是單純 increasing/decreasing ，回傳 Boolean
```

```
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 <= A.length <= 50000
-100000 <= A[i] <= 100000

/**
 * @param {number[]} A
 * @return {boolean}
 */
var isMonotonic = function(A) {
    
};
```

### 怎麼解

要馬就是 increasing，要馬就是 decreasing&#x20;

```
var isMonotonic = function(A) {
  let pointer = A[0];
  let ind = 1;
  // 先用這個判斷 A 到底是 increasing or decreasing
  while(pointer == A[ind]){
      pointer = A[ind];
      ind ++ ;
  }
  // increasing
  if(pointer <  A[ind]){
      for(let i = 1; i< A.length - 1; i++){
          if( A[i] > A[i+1]){
              return false
          }
      }
  }
  // decreasing
  if(pointer >  A[ind]){
      for(let i = 1; i< A.length - 1; i++){
          if( A[i] < A[i+1]){
              return false
          }
      }
  }
  return true
};

// Runtime: 76 ms, faster than 60.32% 
```
