dp[i]is the longest length ending with
- But if we use normal DP, there will be a double for loop, which leads to TLE.
- Because we are looking for an
arithmetic progression. We can know what the
prev numshould be by
- If we use a
mapto store each other, then we can know if
map.get(cur - diff)exist or not.
- This saves us lots of time.
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.
A subsequence is a sequence that can be derived from arr by deleting some or no elements without changing the order of the remaining elements.
Input: arr = [1,3,5,7], difference = 1