3105. Longest Strictly Increasing or Strictly Decreasing Subarray

Easy

題目描述

Description

You are given an array of integers nums. Return the length of the longest subarray of nums which is either strictly increasing or strictly decreasing .

Example 1:

Input: nums = [1,4,3,3,2]

Output: 2

Explanation:

The strictly increasing subarrays of nums are [1], [2], [3], [3], [4], and [1,4].

The strictly decreasing subarrays of nums are [1], [2], [3], [3], [4], [3,2], and [4,3].

Hence, we return 2.

Example 2:

Input: nums = [3,3,3,3]

Output: 1

Explanation:

The strictly increasing subarrays of nums are [3], [3], [3], and [3].

The strictly decreasing subarrays of nums are [3], [3], [3], and [3].

Hence, we return 1.

Example 3:

Input: nums = [3,2,1]

Output: 3

Explanation:

The strictly increasing subarrays of nums are [3], [2], and [1].

The strictly decreasing subarrays of nums are [3], [2], [1], [3,2], [2,1], and [3,2,1].

Hence, we return 3.

Constraints:

1 <= nums.length <= 50
1 <= nums[i] <= 50

解答

Solution

/**
 * @param {number[]} nums
 * @return {number}
 */
var longestMonotonicSubarray = function (nums) {
  let increase = 1;
  let decrease = 1;
  let maxLen = 1;

  for (i = 1; i < nums.length; i++) {
    if (nums[i] > nums[i - 1]) {
      increase++;
      decrease = 1;
    } else if (nums[i] < nums[i - 1]) {
      decrease++;
      increase = 1;
    } else {
      increase = 1;
      decrease = 1;
    }
    maxLen = Math.max(maxLen, increase, decrease);
  }

  return maxLen;
};

解題思路

要找出陣列中最長的嚴格遞增 or 遞減長度，所以用 maxLen 變數來記住。解法就暴力解定義 increase = 1 ; decrease = 1 ，之後遍歷陣列比較第 i 個和 i-1 個誰大誰小，如果都一樣的話 increase、decrease 都重置回 1。

心得

題目不太直覺，就算解出來還是不太懂為啥 Example 2 的 [3,3,3,3] 會是 1 不是 0 ，要...惡補...資料結構...ㄌ...