3201. Find the Maximum Length of Valid Subsequence I

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3201. Find the Maximum Length of Valid Subsequence I

Description

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.

Example 1:

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

Output: 4

Explanation:

The longest valid subsequence is `[1, 2, 3, 4]`.

Example 2:

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

Output: 6

Explanation:

The longest valid subsequence is `[1, 2, 1, 2, 1, 2]`.

Example 3:

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Input: nums = [1,3]

Output: 2

Explanation:

The longest valid subsequence is `[1, 3]`.

Constraints:

  • 2 <= nums.length <= 2 * 10^5
  • 1 <= nums[i] <= 10^7

Hints/Notes

  • Weekly Contest 404

Solution

Language: C++

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class Solution {
public:
    int maximumLength(vector<int>& nums) {
        int allEven = 0, allOdd = 0, prevEven = 0, prevOdd = 0;
        for (int num : nums) {
            if (num % 2 == 0) {
                allEven++;
                prevEven = prevOdd + 1;
            } else {
                allOdd++;
                prevOdd = prevEven + 1;
            }
        }
        return max(allEven, max(allOdd, max(prevEven, prevOdd)));
    }
};