exercises(list-ops): implement

config.json

@@ -953,6 +953,14 @@
           "integers"
         ]
       },
+      {
+        "slug": "list-ops",
+        "name": "List Ops",
+        "uuid": "779343ba-9b40-4d43-b696-2267c4eecde0",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
+      },
       {
         "slug": "linked-list",
         "name": "Linked List",

exercises/practice/list-ops/.docs/instructions.md

@@ -0,0 +1,19 @@
+# Instructions
+
+Implement basic list operations.
+
+In functional languages list operations like `length`, `map`, and `reduce` are very common.
+Implement a series of basic list operations, without using existing functions.
+
+The precise number and names of the operations to be implemented will be track dependent to avoid conflicts with existing names, but the general operations you will implement include:
+
+- `append` (_given two lists, add all items in the second list to the end of the first list_);
+- `concatenate` (_given a series of lists, combine all items in all lists into one flattened list_);
+- `filter` (_given a predicate and a list, return the list of all items for which `predicate(item)` is True_);
+- `length` (_given a list, return the total number of items within it_);
+- `map` (_given a function and a list, return the list of the results of applying `function(item)` on all items_);
+- `foldl` (_given a function, a list, and initial accumulator, fold (reduce) each item into the accumulator from the left_);
+- `foldr` (_given a function, a list, and an initial accumulator, fold (reduce) each item into the accumulator from the right_);
+- `reverse` (_given a list, return a list with all the original items, but in reversed order_).
+
+Note, the ordering in which arguments are passed to the fold functions (`foldl`, `foldr`) is significant.

exercises/practice/list-ops/.meta/config.json

@@ -0,0 +1,17 @@
+{
+  "authors": [
+    "Norbiox"
+  ],
+  "files": {
+    "solution": [
+      "list_ops.nim"
+    ],
+    "test": [
+      "test_list_ops.nim"
+    ],
+    "example": [
+      ".meta/example.nim"
+    ]
+  },
+  "blurb": "Implement basic list operations."
+}

exercises/practice/list-ops/.meta/example.nim

@@ -0,0 +1,49 @@
+func append*(list1, list2: seq[int]): seq[int] =
+  if list2.len == 0:
+    return list1
+  result = newSeq[int](list1.len + list2.len)
+  var i = 0
+  for x in list1:
+    result[i] = x
+    inc i
+  for x in list2:
+    result[i] = x
+    inc i
+
+func concatenate*(lists: openArray[seq[int]]): seq[int] =
+  result = @[]
+  for list in lists:
+    result = append(result, list)
+
+func filter*(list: openArray[int], predicate: proc(x: int): bool {.noSideEffect.}): seq[int] =
+  result = @[]
+  for x in list:
+    if predicate(x):
+      result.add x
+
+func length*(list: openArray[int]): int =
+  list.len
+
+func map*(list: openArray[int], function: proc(x: int): int {.noSideEffect.}): seq[int] =
+  result = newSeq[int](list.len)
+  for i, x in list:
+    result[i] = function(x)
+
+func foldl*(list: openArray[int], function: proc(x, y: int): int {.noSideEffect.},
+            accumulator: int): int =
+  if list.len == 0:
+    accumulator
+  else:
+    foldl(list.toOpenArray(1, list.high), function, function(accumulator, list[0]))
+
+func foldr*(list: openArray[int], function: proc(x, y: int): int {.noSideEffect.},
+            accumulator: int): int =
+  if list.len == 0:
+    accumulator
+  else:
+    function(foldr(list.toOpenArray(1, list.high), function, accumulator), list[0])
+
+func reverse*(list: openArray[int]): seq[int] =
+  result = newSeq[int](list.len)
+  for i, x in list:
+    result[list.high - i] = x

exercises/practice/list-ops/.meta/tests.toml

@@ -0,0 +1,108 @@
+# 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.
+
+[485b9452-bf94-40f7-a3db-c3cf4850066a]
+description = "append entries to a list and return the new list -> empty lists"
+
+[2c894696-b609-4569-b149-8672134d340a]
+description = "append entries to a list and return the new list -> list to empty list"
+
+[e842efed-3bf6-4295-b371-4d67a4fdf19c]
+description = "append entries to a list and return the new list -> empty list to list"
+
+[71dcf5eb-73ae-4a0e-b744-a52ee387922f]
+description = "append entries to a list and return the new list -> non-empty lists"
+
+[28444355-201b-4af2-a2f6-5550227bde21]
+description = "concatenate a list of lists -> empty list"
+
+[331451c1-9573-42a1-9869-2d06e3b389a9]
+description = "concatenate a list of lists -> list of lists"
+
+[d6ecd72c-197f-40c3-89a4-aa1f45827e09]
+description = "concatenate a list of lists -> list of nested lists"
+include = false
+
+[0524fba8-3e0f-4531-ad2b-f7a43da86a16]
+description = "filter list returning only values that satisfy the filter function -> empty list"
+
+[88494bd5-f520-4edb-8631-88e415b62d24]
+description = "filter list returning only values that satisfy the filter function -> non-empty list"
+
+[1cf0b92d-8d96-41d5-9c21-7b3c37cb6aad]
+description = "returns the length of a list -> empty list"
+
+[d7b8d2d9-2d16-44c4-9a19-6e5f237cb71e]
+description = "returns the length of a list -> non-empty list"
+
+[c0bc8962-30e2-4bec-9ae4-668b8ecd75aa]
+description = "return a list of elements whose values equal the list value transformed by the mapping function -> empty list"
+
+[11e71a95-e78b-4909-b8e4-60cdcaec0e91]
+description = "return a list of elements whose values equal the list value transformed by the mapping function -> non-empty list"
+
+[613b20b7-1873-4070-a3a6-70ae5f50d7cc]
+description = "folds (reduces) the given list from the left with a function -> empty list"
+include = false
+
+[e56df3eb-9405-416a-b13a-aabb4c3b5194]
+description = "folds (reduces) the given list from the left with a function -> direction independent function applied to non-empty list"
+include = false
+
+[d2cf5644-aee1-4dfc-9b88-06896676fe27]
+description = "folds (reduces) the given list from the left with a function -> direction dependent function applied to non-empty list"
+include = false
+
+[36549237-f765-4a4c-bfd9-5d3a8f7b07d2]
+description = "folds (reduces) the given list from the left with a function -> empty list"
+reimplements = "613b20b7-1873-4070-a3a6-70ae5f50d7cc"
+
+[7a626a3c-03ec-42bc-9840-53f280e13067]
+description = "folds (reduces) the given list from the left with a function -> direction independent function applied to non-empty list"
+reimplements = "e56df3eb-9405-416a-b13a-aabb4c3b5194"
+
+[d7fcad99-e88e-40e1-a539-4c519681f390]
+description = "folds (reduces) the given list from the left with a function -> direction dependent function applied to non-empty list"
+reimplements = "d2cf5644-aee1-4dfc-9b88-06896676fe27"
+
+[aeb576b9-118e-4a57-a451-db49fac20fdc]
+description = "folds (reduces) the given list from the right with a function -> empty list"
+include = false
+
+[c4b64e58-313e-4c47-9c68-7764964efb8e]
+description = "folds (reduces) the given list from the right with a function -> direction independent function applied to non-empty list"
+include = false
+
+[be396a53-c074-4db3-8dd6-f7ed003cce7c]
+description = "folds (reduces) the given list from the right with a function -> direction dependent function applied to non-empty list"
+include = false
+
+[17214edb-20ba-42fc-bda8-000a5ab525b0]
+description = "folds (reduces) the given list from the right with a function -> empty list"
+reimplements = "aeb576b9-118e-4a57-a451-db49fac20fdc"
+
+[e1c64db7-9253-4a3d-a7c4-5273b9e2a1bd]
+description = "folds (reduces) the given list from the right with a function -> direction independent function applied to non-empty list"
+reimplements = "c4b64e58-313e-4c47-9c68-7764964efb8e"
+
+[8066003b-f2ff-437e-9103-66e6df474844]
+description = "folds (reduces) the given list from the right with a function -> direction dependent function applied to non-empty list"
+reimplements = "be396a53-c074-4db3-8dd6-f7ed003cce7c"
+
+[94231515-050e-4841-943d-d4488ab4ee30]
+description = "reverse the elements of the list -> empty list"
+
+[fcc03d1e-42e0-4712-b689-d54ad761f360]
+description = "reverse the elements of the list -> non-empty list"
+
+[40872990-b5b8-4cb8-9085-d91fc0d05d26]
+description = "reverse the elements of the list -> list of lists is not flattened"
+include = false

exercises/practice/list-ops/list_ops.nim

@@ -0,0 +1,23 @@
+proc append*(list1, list2: seq[int]): seq[int] =
+  discard
+
+proc concatenate*(lists: seq[seq[int]]): seq[int] =
+  discard
+
+proc filter*(list: seq[int], predicate: proc(x: int): bool): seq[int] =
+  discard
+
+proc length*(list: seq[int]): int =
+  discard
+
+proc map*(list: seq[int], function: proc(x: int): int): seq[int] =
+  discard
+
+proc foldl*(list: seq[int], function: proc(x, y: int): int, accumulator: int): int =
+  discard
+
+proc foldr*(list: seq[int], function: proc(x, y: int): int, accumulator: int): int =
+  discard
+
+proc reverse*(list: seq[int]): seq[int] =
+  discard

exercises/practice/list-ops/test_list_ops.nim

@@ -0,0 +1,112 @@
+import unittest
+import list_ops
+
+
+suite "append entries to a list and return the new list":
+  test "empty lists":
+    check append(@[], @[]).len == 0
+
+  test "list to empty list":
+    check append(@[], @[1, 2, 3, 4]) == @[1, 2, 3, 4]
+
+  test "empty list to list":
+    check append(@[1, 2, 3, 4], @[]) == @[1, 2, 3, 4]
+
+  test "non-empty lists":
+    check append(@[1, 2], @[2, 3, 4, 5]) == @[1, 2, 2, 3, 4, 5]
+
+
+suite "concatenate a list of lists":
+  test "empty list":
+    check concatenate(@[]).len == 0
+
+  test "list of lists":
+    check concatenate(@[@[1, 2], @[3], @[], @[4, 5, 6]]) == @[1, 2, 3, 4, 5, 6]
+
+
+suite "filter list returning only values that satisfy the filter function":
+  func predicate(x: int): bool = x mod 2 == 1
+
+  test "empty list":
+    check filter(@[], predicate).len == 0
+
+  test "non-empty list":
+    check filter(@[1, 2, 3, 5], predicate) == @[1, 3, 5]
+
+
+suite "returns the length of a list":
+  test "empty list":
+    check length(@[]) == 0
+
+  test "non-empty list":
+    check length(@[1, 2, 3, 4]) == 4
+
+
+suite "return a list of elements whose values equal the list value transformed by the mapping function":
+  func function(x: int): int = x + 1
+
+  test "empty list":
+    check map(@[], function).len == 0
+
+  test "non-empty list":
+    check map(@[1, 3, 5, 7], function) == @[2, 4, 6, 8]
+
+
+suite "folds (reduces) the given list from the left with a function":
+  test "empty list":
+    func function(x: int, y: int): int = x + y
+    check foldl(@[], function, 2) == 2
+
+  test "direction independent function applied to non-empty list":
+    func function(x: int, y: int): int = x + y
+    check foldl(@[1, 2, 3, 4], function, 5) == 15
+
+  test "direction dependent function applied to non-empty list":
+    func function(x: int, y: int): int = x - y
+    check foldl(@[1, 2, 3, 4], function, 24) == 14
+
+  test "empty list":
+    func function(x: int, y: int): int = y + x
+    check foldl(@[], function, 2) == 2
+
+  test "direction independent function applied to non-empty list":
+    func function(x: int, y: int): int = y + x
+    check foldl(@[1, 2, 3, 4], function, 5) == 15
+
+  test "direction dependent function applied to non-empty list":
+    func function(x: int, y: int): int = y - x
+    check foldl(@[1, 2, 3, 4], function, 5) == 7
+
+
+suite "folds (reduces) the given list from the right with a function":
+  test "empty list":
+    func function(x: int, y: int): int = x + y
+    check foldr(@[], function, 2) == 2
+
+  test "direction independent function applied to non-empty list":
+    func function(x: int, y: int): int = x + y
+    check foldr(@[1, 2, 3, 4], function, 5) == 15
+
+  test "direction dependent function applied to non-empty list":
+    func function(x: int, y: int): int = x - y
+    check foldr(@[1, 2, 3, 4], function, 24) == 14
+
+  test "empty list":
+    func function(x: int, y: int): int = y + x
+    check foldr(@[], function, 2) == 2
+
+  test "direction independent function applied to non-empty list":
+    func function(x: int, y: int): int = y + x
+    check foldr(@[1, 2, 3, 4], function, 5) == 15
+
+  test "direction dependent function applied to non-empty list":
+    func function(x: int, y: int): int = y - x
+    check foldr(@[1, 2, 3, 4], function, 5) == 3
+
+
+suite "reverse the elements of the list":
+  test "empty list":
+    check reverse(@[]).len == 0
+
+  test "non-empty list":
+    check reverse(@[1, 2, 3, 4]) == @[4, 3, 2, 1]