add practice exercise change

config.json

@@ -961,6 +961,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 5
+      },
+      {
+        "slug": "change",
+        "name": "Change",
+        "uuid": "7006d489-ca27-4843-9f0b-843e94e5dbd2",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
       }
     ]
   },

exercises/practice/change/.docs/instructions.md

@@ -0,0 +1,14 @@
+# Instructions
+
+Correctly determine the fewest number of coins to be given to a customer such that the sum of the coins' value would equal the correct amount of change.
+
+## For example
+
+- An input of 15 with [1, 5, 10, 25, 100] should return one nickel (5) and one dime (10) or [5, 10]
+- An input of 40 with [1, 5, 10, 25, 100] should return one nickel (5) and one dime (10) and one quarter (25) or [5, 10, 25]
+
+## Edge cases
+
+- Does your algorithm work for any given set of coins?
+- Can you ask for negative change?
+- Can you ask for a change value smaller than the smallest coin value?

exercises/practice/change/.meta/config.json

@@ -0,0 +1,17 @@
+{
+  "authors": [],
+  "files": {
+    "solution": [
+      "change.jl"
+    ],
+    "test": [
+      "runtests.jl"
+    ],
+    "example": [
+      ".meta/example.jl"
+    ]
+  },
+  "blurb": "Correctly determine change to be given using the least number of coins.",
+  "source": "Software Craftsmanship - Coin Change Kata",
+  "source_url": "https://web.archive.org/web/20130115115225/http://craftsmanship.sv.cmu.edu:80/exercises/coin-change-kata"
+}

exercises/practice/change/.meta/example.jl

@@ -0,0 +1,18 @@
+function change(coins, target)
+    memo = Dict(0 => (0, 0))
+    for n in 1:target
+        mincoins, previousn = minimum([(first(get(memo, prevn, (Inf, 0))), prevn) for prevn in n .- coins])
+        mincoins < Inf && (memo[n] = (mincoins+1, previousn))
+    end
+
+    !haskey(memo, target) && throw(DomainError(target, "Not Possible"))
+
+    changeback, previoustarget = [], Inf
+    while 0 < target
+        previoustarget = last(memo[target])
+        push!(changeback, target - previoustarget)
+        target = previoustarget
+    end
+
+    reverse!(changeback)
+end

exercises/practice/change/.meta/tests.toml

@@ -0,0 +1,49 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[d0ebd0e1-9d27-4609-a654-df5c0ba1d83a]
+description = "change for 1 cent"
+
+[36887bea-7f92-4a9c-b0cc-c0e886b3ecc8]
+description = "single coin change"
+
+[cef21ccc-0811-4e6e-af44-f011e7eab6c6]
+description = "multiple coin change"
+
+[d60952bc-0c1a-4571-bf0c-41be72690cb3]
+description = "change with Lilliputian Coins"
+
+[408390b9-fafa-4bb9-b608-ffe6036edb6c]
+description = "change with Lower Elbonia Coins"
+
+[7421a4cb-1c48-4bf9-99c7-7f049689132f]
+description = "large target values"
+
+[f79d2e9b-0ae3-4d6a-bb58-dc978b0dba28]
+description = "possible change without unit coins available"
+
+[9a166411-d35d-4f7f-a007-6724ac266178]
+description = "another possible change without unit coins available"
+
+[ce0f80d5-51c3-469d-818c-3e69dbd25f75]
+description = "a greedy approach is not optimal"
+
+[bbbcc154-e9e9-4209-a4db-dd6d81ec26bb]
+description = "no coins make 0 change"
+
+[c8b81d5a-49bd-4b61-af73-8ee5383a2ce1]
+description = "error testing for change smaller than the smallest of coins"
+
+[3c43e3e4-63f9-46ac-9476-a67516e98f68]
+description = "error if no combination can add up to target"
+
+[8fe1f076-9b2d-4f44-89fe-8a6ccd63c8f3]
+description = "cannot find negative change values"

exercises/practice/change/change.jl

@@ -0,0 +1,3 @@
+function change(coins, target)
+    # Your code here
+end

exercises/practice/change/runtests.jl

@@ -0,0 +1,57 @@
+using Test
+
+include("change.jl")
+
+@testset verbose = true "tests" begin
+    @testset "change for 1 cent" begin
+        @test change([1, 5, 10, 25], 1) == [1]
+    end
+
+    @testset "single coin change" begin
+        @test change([1, 5, 10, 25, 100], 25) == [25]
+    end
+
+    @testset "multiple coin change" begin
+        @test change([1, 5, 10, 25, 100], 15) == [5, 10]
+    end
+
+    @testset "change with Lilliputian Coins" begin
+        @test change([1, 4, 15, 20, 50], 23) == [4, 4, 15]
+    end
+
+    @testset "change with Lower Elbonia Coins" begin
+        @test change([1, 5, 10, 21, 25], 63) == [21, 21, 21]
+    end
+
+    @testset "large target values" begin
+        @test change([1, 2, 5, 10, 20, 50, 100], 999) == [2, 2, 5, 20, 20, 50, 100, 100, 100, 100, 100, 100, 100, 100, 100]
+    end
+
+    @testset "possible change without unit coins available" begin
+        @test change([2, 5, 10, 20, 50], 21) == [2, 2, 2, 5, 10]
+    end
+
+    @testset "another possible change without unit coins available" begin
+        @test change([4, 5], 27) == [4, 4, 4, 5, 5, 5]
+    end
+
+    @testset "a greedy approach is not optimal" begin
+        @test change([1, 10, 11], 20) == [10, 10]
+    end
+
+    @testset "no coins make 0 change" begin
+        @test change([1, 5, 10, 21, 25], 0) == []
+    end
+
+    @testset "error testing for change smaller than the smallest of coins" begin
+        @test_throws DomainError change([5, 10], 3)
+    end
+
+    @testset "error if no combination can add up to target" begin
+        @test_throws DomainError change([5, 10], 94)
+    end
+
+    @testset "cannot find negative change values" begin
+        @test_throws DomainError change([1, 2, 5], -5)
+    end
+end