2023-07-14 Daily Challenge

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Today I have done leetcode's July LeetCoding Challenge with cpp.

July LeetCoding Challenge 14

Description

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.

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.

 

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].

 

Constraints:

  • 1 <= arr.length <= 105
  • -104 <= arr[i], difference <= 104

Solution

class Solution {
public:
  int longestSubsequence(vector<int>& arr, int difference) {
    map<int, int> existSubsequence;
    int answer = 0;
    for(auto i : arr) {
      existSubsequence[i] = max(existSubsequence[i], existSubsequence[i - difference] + 1);
      answer = max(answer, existSubsequence[i]);
    }

    return answer;
  }
};

// Accepted
// 39/39 cases passed (359 ms)
// Your runtime beats 5.03 % of cpp submissions
// Your memory usage beats 10.76 % of cpp submissions (57.6 MB)
Algorithm