Added the solution for Longest consecutive subsequence from gfg

C++/Longest Subs.cpp

@@ -0,0 +1,42 @@
+// 450dsa q24 : Given an array of positive integers. Find the length of the longest sub-sequence such that elements in the subsequence are consecutive integers, the consecutive numbers can be in any order.
+
+#include <bits/stdc++.h>
+using namespace std;
+
+int longest_consecutive_subarray(int arr[], int n)
+{
+    unordered_set<int> s;
+    for (int i = 0; i < n; i++)
+    {
+        s.insert(arr[i]);
+    }
+    int ans = 0;
+    for (auto i = s.begin(); i != s.end(); i++)
+    {
+        if (s.find(*i - 1) == s.end())
+        {
+            int num = *i;
+            int count = 0;
+            while (s.find(num) != s.end())
+            {
+                count++;
+                num++;
+            }
+            ans = max(ans, count);
+        }
+    }
+    return ans;
+}
+
+int main()
+{
+    int n;
+    cin >> n;
+    int arr[n];
+    for (int i = 0; i < n; i++)
+    {
+        cin >> arr[i];
+    }
+    cout << longest_consecutive_subarray(arr, n);
+    return 0;
+}