LeetCode in Kotlin

1027. Longest Arithmetic Subsequence

Medium

Given an array nums of integers, return the length of the longest arithmetic subsequence in nums.

Note that:

• 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.
• A sequence seq is arithmetic if seq[i + 1] - seq[i] are all the same value (for 0 <= i < seq.length - 1).

Example 1:

Input: nums = [3,6,9,12]

Output: 4 **Explanation: ** The whole array is an arithmetic sequence with steps of length = 3.

Example 2:

Input: nums = [9,4,7,2,10]

Output: 3 **Explanation: ** The longest arithmetic subsequence is [4,7,10].

Example 3:

Input: nums = [20,1,15,3,10,5,8]

Output: 4 **Explanation: ** The longest arithmetic subsequence is [20,15,10,5].

Constraints:

• 2 <= nums.length <= 1000
• 0 <= nums[i] <= 500

Solution

class Solution {
    fun longestArithSeqLength(nums: IntArray): Int {
        val max = maxElement(nums)
        val min = minElement(nums)
        val diff = max - min
        val n = nums.size
        val dp = Array(n) { IntArray(2 * diff + 2) }
        for (d in dp) {
            d.fill(1)
        }
        var ans = 0
        for (i in 0 until n) {
            for (j in i - 1 downTo 0) {
                val difference = nums[i] - nums[j] + diff
                val temp = dp[j][difference]
                dp[i][difference] = Math.max(dp[i][difference], temp + 1)
                if (ans < dp[i][difference]) {
                    ans = dp[i][difference]
                }
            }
        }
        return ans
    }

    private fun maxElement(arr: IntArray): Int {
        var max = Int.MIN_VALUE
        for (e in arr) {
            if (max < e) {
                max = e
            }
        }
        return max
    }

    private fun minElement(arr: IntArray): Int {
        var min = Int.MAX_VALUE
        for (e in arr) {
            if (min > e) {
                min = e
            }
        }
        return min
    }
}

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