cpp: add “242. Valid Anagram”

Signed-off-by: Matej Focko <me@mfocko.xyz>

cpp/valid-anagram.cpp

@@ -0,0 +1,26 @@
+#include <algorithm>
+#include <array>
+#include <string>
+
+class Solution {
+public:
+    bool isAnagram(const std::string& s, const std::string& t) {
+        std::array<int, 26> counter{};
+
+        for (char c : s) {
+            counter[c - 'a']++;
+        }
+
+        for (char c : t) {
+            counter[c - 'a']--;
+
+            if (counter[c - 'a'] < 0) {
+                return false;
+            }
+        }
+
+        return std::all_of(counter.begin(), counter.end(), [](auto c) {
+            return c == 0;
+        });
+    }
+};