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Merge pull request #22 from TheAlgorithms/fr33m0nk/add-dynamic-array
Adds Dynamic array implementation
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‎DIRECTORY.md

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* [Sublist of a list by consecutive repetitions](https://github.com/TheAlgorithms/Clojure/blob/main/src/data_structures/lists/pack_consecutive_repetitions_in_sublist.clj)
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* [Run length encoding](https://github.com/TheAlgorithms/Clojure/blob/main/src/data_structures/lists/run_length_encoding.clj)
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* [Dynamic Array implementation](/src/data_structures/dynamic_array/core.clj)
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## Sorting
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* [Merge Sort](https://github.com/TheAlgorithms/Clojure/blob/main/src/sorts/merge_sort.clj)
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* [Quick Sort](https://github.com/TheAlgorithms/Clojure/blob/main/src/sorts/quick_sort.clj)

‎src/data_structures/dynamic_array/core.clj

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(ns data-structures.dynamic-array.core
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(:refer-clojure :exclude [get set empty? remove pop]))
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;; See tests for the documentation on implementation
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(defprotocol IDynamicArray
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(get [this idx])
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(set [this idx value])
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(remove [this idx])
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(empty? [this])
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(length [this])
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(next-idx [this])
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(append [this value])
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(pop [this]))
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(deftype DynamicArray [^:unsynchronized-mutable length
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^:unsynchronized-mutable next-idx
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^:unsynchronized-mutable array]
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IDynamicArray
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(get [_ idx]
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(assert (< -1 idx next-idx) "Invalid index value supplied")
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(aget array idx))
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(set [_ idx value]
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(assert (<= 0 idx) "Invalid index value supplied")
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(when (or (= next-idx length) (> idx length))
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(let [next-length (* idx 2)
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next-array (make-array Integer/TYPE next-length)]
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(doseq [i (range length)]
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(->> (aget array i)
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(aset next-array i)))
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(set! array next-array)
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(set! length next-length)))
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(aset array next-idx value)
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(set! next-idx (inc idx))
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idx)
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(remove [_ idx]
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(assert (< -1 idx next-idx) "Invalid index value supplied")
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(let [next-next-idx (dec next-idx)
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popped-element (aget array idx)]
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(doseq [dest-idx (range idx next-idx)
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:let [source-idx (inc dest-idx)]
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:when (not= source-idx length)]
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(aset array dest-idx (aget array source-idx)))
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(set! next-idx next-next-idx)
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popped-element))
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(empty? [_]
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(zero? next-idx))
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(length [_]
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(alength array))
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(next-idx [this]
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next-idx)
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(append [_ value]
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(when (= next-idx length)
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(let [next-length (* length 2)
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next-array (make-array Integer/TYPE next-length)]
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(doseq [i (range length)]
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(->> (aget array i)
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(aset next-array i)))
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(set! array next-array)
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(set! length next-length)))
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(let [old-capacity next-idx]
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(aset array next-idx value)
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(set! next-idx (inc next-idx))
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old-capacity))
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(pop [_]
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(assert (> next-idx 0) "Nothing to pop")
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(let [next-next-idx (dec next-idx)
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popped-element (aget array next-next-idx)]
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(aset array next-next-idx 0)
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(set! next-idx next-next-idx)
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popped-element))
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Object
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(toString [_]
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(let [^StringBuilder sb (StringBuilder.)]
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(.append sb "[ ")
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(doseq [i (range next-idx)]
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(.append sb (aget array i))
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(.append sb " "))
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(.append sb "]")
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(.toString sb))))
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(defn ->DynamicArray
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[initial-capacity]
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(when (>= 0 initial-capacity)
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(throw (IllegalArgumentException. "Invalid initial capacity")))
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(DynamicArray. initial-capacity 0 (make-array Integer/TYPE initial-capacity)))

‎test/data_structures/dynamic_array/core_test.clj

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(ns data-structures.dynamic-array.core-test
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(:require [clojure.test :refer [deftest testing is]]
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[data-structures.dynamic-array.core :as da]))
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(deftest ->DynamicArray-test
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(testing "throws when invalid initial capacity is provided"
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(is (thrown? IllegalArgumentException (da/->DynamicArray 0)))
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(is (thrown? IllegalArgumentException (da/->DynamicArray -1)))))
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(deftest empty?-test
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(testing "return true if dynamic array is empty"
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(let [dynamic-array (da/->DynamicArray 3)]
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(is (true? (da/empty? dynamic-array)))))
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(testing "return false if dynamic array is empty"
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(let [dynamic-array (da/->DynamicArray 3)]
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(da/set dynamic-array (da/next-idx dynamic-array) 20)
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(da/set dynamic-array (da/next-idx dynamic-array) 30)
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(is (false? (da/empty? dynamic-array))))))
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(deftest length-test
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(testing "returns initial capacity till dynamic array is full"
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(let [dynamic-array (da/->DynamicArray 3)]
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(is (= 3 (da/length dynamic-array)))))
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(testing "returns expanded capacity once storage demands exceeds initial capacity"
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(let [dynamic-array (da/->DynamicArray 3)]
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(da/set dynamic-array (da/next-idx dynamic-array) 10)
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(da/set dynamic-array (da/next-idx dynamic-array) 20)
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(da/set dynamic-array (da/next-idx dynamic-array) 30)
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(da/set dynamic-array (da/next-idx dynamic-array) 40)
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(is (= 6 (da/length dynamic-array))))))
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(deftest next-idx-test
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(testing "returns initial index as the starting point when dynamic array is empty"
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(let [dynamic-array (da/->DynamicArray 3)]
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(is (= 0 (da/next-idx dynamic-array)))))
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(testing "returns current filled index as the starting point when dynamic array is empty"
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(let [dynamic-array (da/->DynamicArray 3)]
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(da/set dynamic-array (da/next-idx dynamic-array) 10)
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(da/set dynamic-array (da/next-idx dynamic-array) 20)
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(da/set dynamic-array (da/next-idx dynamic-array) 30)
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(is (= 3 (da/next-idx dynamic-array))))))
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(deftest set-test
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(let [dynamic-array (da/->DynamicArray 3)]
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(testing "throws Assertion error when index is less than 0"
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(is (thrown? AssertionError (da/set dynamic-array -1 10))))
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(testing "stores the element within the dynamic array when a valid index is provided"
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(da/set dynamic-array (da/next-idx dynamic-array) 10)
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(is (false? (da/empty? dynamic-array)))
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(is (= 1 (da/next-idx dynamic-array))))
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(testing "expands dynamic array to incorporate more elements"
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(da/set dynamic-array (da/next-idx dynamic-array) 20)
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(da/set dynamic-array (da/next-idx dynamic-array) 30)
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(da/set dynamic-array (da/next-idx dynamic-array) 40)
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(is (= 4 (da/next-idx dynamic-array)))
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(is (= 6 (da/length dynamic-array))))
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(testing "expands dynamic array to incorporate for an arbitrary large index and sets next-idx accordingly"
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(da/set dynamic-array 60 40)
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(is (= 61 (da/next-idx dynamic-array)) "This behaviour causes fragmentation in the dynamic array")
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(is (= 120 (da/length dynamic-array))))))
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(deftest get-test
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(let [dynamic-array (da/->DynamicArray 3)]
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(testing "throws Assertion error when index is less than 0"
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(is (thrown? AssertionError (da/get dynamic-array -1))))
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(testing "throws Assertion error when index is greater than next-index"
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(is (thrown? AssertionError (da/get dynamic-array (inc (da/next-idx dynamic-array))))))
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(testing "fetches the content of the dynamic array stored at valid index"
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(da/set dynamic-array (da/next-idx dynamic-array) 40)
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(is (= 40 (da/get dynamic-array (dec (da/next-idx dynamic-array))))))))
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(deftest remove-test
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(let [dynamic-array (da/->DynamicArray 3)]
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(testing "throws Assertion error when index is less than 0"
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(is (thrown? AssertionError (da/remove dynamic-array -1))))
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(testing "throws Assertion error when index is greater than next index"
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(is (thrown? AssertionError (da/remove dynamic-array (inc (da/next-idx dynamic-array))))))
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(testing "removes the element from the dynamic array and returns it if the index is valid"
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(da/set dynamic-array (da/next-idx dynamic-array) 10)
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(da/set dynamic-array (da/next-idx dynamic-array) 20)
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(da/set dynamic-array (da/next-idx dynamic-array) 30)
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(da/set dynamic-array (da/next-idx dynamic-array) 40)
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(is (= 4 (da/next-idx dynamic-array)) "Sanity check to ensure that next-index is correctly calculated")
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(is (= 30 (da/remove dynamic-array 2)))
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(is (= 3 (da/next-idx dynamic-array)))
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(is (= "[ 10 20 40 ]" (.toString dynamic-array))))))
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(deftest append-test
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(let [dynamic-array (da/->DynamicArray 3)]
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(testing "appends values to dynamic array"
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(da/set dynamic-array (da/next-idx dynamic-array) 10)
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(da/set dynamic-array (da/next-idx dynamic-array) 20)
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(is (= 2 (da/next-idx dynamic-array)))
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(is (= 3 (da/length dynamic-array))))
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(testing "expands dynamic array to allocate more elements"
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(da/set dynamic-array (da/next-idx dynamic-array) 30)
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(da/set dynamic-array (da/next-idx dynamic-array) 40)
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(is (= 4 (da/next-idx dynamic-array)))
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(is (= 6 (da/length dynamic-array))))))
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(deftest pop-test
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(let [dynamic-array (da/->DynamicArray 3)]
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(testing "throws when the dynamic array is empty"
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(is (thrown? AssertionError (da/pop dynamic-array))))
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(testing "pops the element from dynamic array and returns it"
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(da/set dynamic-array (da/next-idx dynamic-array) 10)
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(da/set dynamic-array (da/next-idx dynamic-array) 20)
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(da/set dynamic-array (da/next-idx dynamic-array) 30)
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(is (= 30 (da/pop dynamic-array)))
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(is (= 2 (da/next-idx dynamic-array))))))
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(deftest toString-test
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(testing "provides string representation of an empty array"
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(let [dynamic-array (da/->DynamicArray 3)]
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(is (= "[ ]" (.toString dynamic-array)))))
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(testing "provides string representation of a non empty array"
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(let [dynamic-array (da/->DynamicArray 10)]
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(doseq [i (range 10 15)]
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(da/append dynamic-array i))
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(is (= "[ 10 11 12 13 14 ]" (.toString dynamic-array))))))

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