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#2210 - Count Hills and Valleys in an Array
Problem Description
You are given a 0-indexed integer array nums. An index i is part of a hill in nums if the closest non-equal neighbors of i are smaller than nums[i]. Similarly, an index i is part of a valley in nums if the closest non-equal neighbors of i are larger than nums[i].
Adjacent indices i and j are part of the same hill or valley if nums[i] == nums[j].
Note that for an index to be part of a hill or valley, it must have a non-equal neighbor on both the left and right of the index.
Return the number of hills and valleys in nums.
Solution
/**
* @param {number[]} nums
* @return {number}
*/
var countHillValley = function(nums) {
let count = 0;
let prev = nums[0];
for (let i = 1; i < nums.length - 1; i++) {
if (nums[i] === nums[i + 1]) continue;
const left = prev;
const right = nums[i + 1];
if ((nums[i] > left && nums[i] > right) || (nums[i] < left && nums[i] < right)) {
count++;
}
prev = nums[i];
}
return count;
};