added valid anagram function code

algorithms/CPlusPlus/Arrays/valid-anagram.cpp

@@ -0,0 +1,19 @@
+//Description - Given two strings s and t, return true if t is an anagram of s, and false otherwise.
+
+//Time complexity - O(n logn)
+
+//Approach - we sort the given strings, and we compare each elements of both the strings. If we get elements which are not equal, we return false
+
+
+    bool isAnagram(string s, string t) {
+        sort(s.begin(), s.end());
+        sort(t.begin(), t.end());
+
+        if(s.size()!=t.size()) return false;
+
+        for(int i = 0; i<s.size();i++)
+        {
+            if(s[i]!=t[i]) return false;
+        }
+        return true;
+    }