3201. Find the Maximum Length of Valid Subsequence I

You are given an integer array nums.

A subsequence sub of nums with length x is called valid if it satisfies:

• (sub[0] + sub[1]) % 2 == (sub[1] + sub[2]) % 2 == ... == (sub[x - 2] + sub[x - 1]) % 2.

Return the length of the longest valid subsequence of nums.

A subsequence is an array that can be derived from another array by deleting some or no elements without changing the order of the remaining elements.

class Solution {
    int helper(vector<int>& A, int a, int b) {
        int res = 0;
        for(int i = 0; i < A.size(); i++) {
            if(A[i] % 2 == a) {
                res++;
                swap(a,b);
            }
        }
        return res;
    }
public:
    int maximumLength(vector<int>& A) {
        int res = 0;
        for(int i = 0; i <= 1; i++) for(int j = 0; j <= 1; j++) {
            res = max(res, helper(A,i,j));
        }
        return res;
    }
};