最长等差数列

/*
  Solution Approach in Java Stream:
  1. The same approach as the Java solution can be applied using Java Streams for initialization and computation.
  2. Use Stream API to create and initialize the dp array with HashMaps.
  3. Use nested loops with Stream API operations to calculate the longest arithmetic subsequence.
*/
import java.util.*;
import java.util.stream.*;

public class Solution {
    public int longestArithSeqLength(int[] nums) {
        int n = nums.length;
        if (n <= 2) return n;
        int maxLength = 2;
        List<Map<Integer, Integer>> dp = IntStream.range(0, n)
            .mapToObj(i -> new HashMap<Integer, Integer>())
            .collect(Collectors.toList());
        for (int i = 1; i < n; i++) {
            for (int j = 0; j < i; j++) {
                int diff = nums[i] - nums[j];
                dp.get(i).put(diff, dp.get(j).getOrDefault(diff, 1) + 1);
                maxLength = Math.max(maxLength, dp.get(i).get(diff));
            }
        }
        return maxLength;
    }
}