Add valid anagram solution

Author: hyunjung-choi

valid-anagram/hyunjung-choi.kt

@@ -0,0 +1,19 @@
+class Solution {
+    fun isAnagram(s: String, t: String): Boolean {
+        if (s.length != t.length) return false
+
+        val charCount = mutableMapOf<Char, Int>()
+
+        s.forEach { ch ->
+            charCount.put(ch, charCount.getOrDefault(ch, 0) + 1)
+        }
+
+        t.forEach { ch ->
+            val count = charCount.getOrDefault(ch, 0)
+            if (count == 0) return false
+            charCount[ch] = count - 1
+        }
+
+        return true
+    }
+}