Merge pull request #137 from MrPhantomT/feature/add_first_repeating_e…

…lement_problem

add first repeating element problem

source/first_repeating_element.yml

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+---
+level: easy
+tags: []
+description: |
+  Given an array of integers, find the first repeating element in it.
+  We need to find the element that occurs more than once and whose index of first occurrence is smallest.
+
+multicode_checks:
+  langs: [ruby, python, javascript, php]

test/battle_solutions/first_repeating_element_test.clj

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+(ns battle-solutions.first-repeating-element-test
+  (:require [clojure.test :refer :all]
+            [battle-asserts.test-helper :refer :all]))
+
+(defn first-repeating-element [array]
+  (->>
+   array
+   (reduce #(assoc %1 %2 (inc (get %1 %2 0))) {})
+   (filter #(> (second %) 1))
+   ffirst))
+
+(deftest test-asserts
+  (assert-equal 5, (first-repeating-element [10 5 3 4 3 5 6]))
+  (assert-equal 6, (first-repeating-element [6 10 5 4 9 120 4 6 10]))
+  (assert-equal 7, (first-repeating-element [6 10 7 4 9 120 4 7]))
+  (assert-equal 8, (first-repeating-element [8 8 7 4 9 120 4 7])))