1218. Longest Arithmetic Subsequence of Given Difference
1218. Longest Arithmetic Subsequence of Given Difference
Given an integer array arr and an integer difference, return the length of the longest subsequence in arr
which is an arithmetic sequence such that the difference between adjacent elements in the subsequence
equals difference.
Example 1:
Input: arr = [1,2,3,4], difference = 1
Output: 4
Explanation: The longest arithmetic subsequence is [1,2,3,4].
Example 2:
Input: arr = [1,3,5,7], difference = 1
Output: 1
Explanation: The longest arithmetic subsequence is any single element.
Example 3:
Input: arr = [1,5,7,8,5,3,4,2,1], difference = -2
Output: 4
Explanation: The longest arithmetic subsequence is [7,5,3,1].
- HashMap < value, length of valid sequence ends at this value>
class Solution {
public int longestSubsequence(int[] arr, int d) {
int result = 1;
HashMap<Integer, Integer> map = new HashMap<>();
for(int i = 0; i < arr.length; i++) {
if(map.containsKey(arr[i]-d)) {
map.put(arr[i], map.get(arr[i]-d)+1);
} else {
map.put(arr[i], 1);
}
result = Math.max(result, map.get(arr[i]));
}
return result;
}
}