Create longest-arithmetic-subsequence-of-given-difference.cpp

Author: kamyu104

C++/longest-arithmetic-subsequence-of-given-difference.cpp

@@ -0,0 +1,15 @@
+// Time:  O(n)
+// Space: O(n)
+
+class Solution {
+public:
+    int longestSubsequence(vector<int>& arr, int difference) {
+        int result = 1;
+        unordered_map<int,int> lookup;
+        for (int i = 0 ; i < arr.size() ; ++i){
+            lookup[arr[i]] = lookup[arr[i] - difference] + 1;
+            result = max(result, lookup[arr[i]]);
+        }
+        return result;
+    }
+};