2765. Longest Alternating Subarray

You are given a 0-indexed integer array nums. A subarray s of length m is called alternating if:

• m is greater than 1.
• s1 = s0 + 1.
• The 0-indexed subarray s looks like [s0, s1, s0, s1,...,s(m-1) % 2]. In other words, s1 - s0 = 1, s2 - s1 = -1, s3 - s2 = 1, s4 - s3 = -1, and so on up to s[m - 1] - s[m - 2] = (-1)m.

Return the maximum length of all alternating subarrays present in nums or -1 if no such subarray exists**.

A subarray is a contiguous non-empty sequence of elements within an array.

class Solution {
public:
    int alternatingSubarray(vector<int>& nums) {
        int res = -1, l = 0, r = 0, n = nums.size();
        while(l < n) {
            if(l + 1 < n and nums[l] + 1 == nums[l + 1]) {
                int a = nums[l], b = nums[l+1], cnt = 0;
                while(l < n) {
                    if(nums[l] == a) cnt += 1;
                    else break;
                    swap(a,b);
                    l += 1;
                }
                res = max(res, cnt);
                l -= 1;
            } else l += 1;
        }
        return res;
    }
};