Add q69

src/ex/q069.clj

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+;; https://4clojure.oxal.org/#/problem/069
+
+(ns ex.q069)
+
+(defn ans
+  "Problem 69, Merge with a Function. (restriction: merge-with)"
+  [f m1 & maps]
+  (letfn [(combine
+            [m1 m2]
+            (reduce (fn [m [k v2]]
+                      (if-let [v1 (get m k)]
+                        (assoc m k (f v1 v2))
+                        (assoc m k v2)))
+                    m1 m2))]
+    (reduce combine m1 maps)))

test/ex/q069_test.clj

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+;; https://4clojure.oxal.org/#/problem/069
+
+(ns ex.q069-test
+  (:require [clojure.test :as t]
+            [ex.q069 :as sut]))
+
+(t/deftest test-q69
+  (t/testing "Problem 69, Merge with a Function"
+    (t/is (= {:a 4, :b 6, :c 20}
+             (sut/ans * {:a 2, :b 3, :c 4} {:a 2} {:b 2} {:c 5})))
+    ;; (t/is (= {1 7, 2 10, 3 15}
+    ;;          (sut/ans - {1 10, 2 20} {1 3, 2 10, 3 15})))
+    ;; (t/is (= {:a [3 4 5], :b [6 7], :c [8 9]}
+    ;;          (sut/ans concat {:a [3], :b [6]} {:a [4 5], :c [8 9]} {:b [7]})))
+    ))