LeetCode-in-Java
1027. Longest Arithmetic Subsequence
Medium
Given an array nums of integers, return the length of the longest arithmetic subsequence in nums.
Recall that a subsequence of an array nums is a list nums[i1], nums[i2], ..., nums[ik] with 0 <= i1 < i2 < ... < ik <= nums.length - 1, and that 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 <= 10000 <= nums[i] <= 500
Solution
import java.util.Arrays;
public class Solution {
public int longestArithSeqLength(int[] nums) {
int max = maxElement(nums);
int min = minElement(nums);
int diff = max - min;
int n = nums.length;
int[][] dp = new int[n][2 * diff + 2];
for (int[] d : dp) {
Arrays.fill(d, 1);
}
int ans = 0;
for (int i = 0; i < n; i++) {
for (int j = i - 1; j >= 0; j--) {
int difference = nums[i] - nums[j] + diff;
int 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 int maxElement(int[] arr) {
int max = Integer.MIN_VALUE;
for (Integer e : arr) {
if (max < e) {
max = e;
}
}
return max;
}
private int minElement(int[] arr) {
int min = Integer.MAX_VALUE;
for (Integer e : arr) {
if (min > e) {
min = e;
}
}
return min;
}
}