problems(js): add “2623. Memoize”

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/memoize.js

@@ -0,0 +1,28 @@
+/**
+ * @param {Function} fn
+ */
+function memoize(fn) {
+    let cache = new Map();
+
+    return function(...args) {
+        let key = JSON.stringify(args);
+
+        if (!cache.has(key)) {
+            cache.set(key, fn(...args));
+        }
+
+        return cache.get(key);
+    }
+}
+
+
+/**
+ * let callCount = 0;
+ * const memoizedFn = memoize(function (a, b) {
+ *	 callCount += 1;
+ *   return a + b;
+ * })
+ * memoizedFn(2, 3) // 5
+ * memoizedFn(2, 3) // 5
+ * console.log(callCount) // 1
+ */