add parallel-letter-frequency, part of 48 in 24

config.json

@@ -878,6 +878,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 6
+      },
+      {
+        "slug": "parallel-letter-frequency",
+        "name": "Parallel Letter Frequency",
+        "uuid": "3daf3903-1eb0-49b9-827a-76e6b7ca25fb",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 8
       }
     ]
   },

exercises/practice/parallel-letter-frequency/.docs/instructions.md

@@ -0,0 +1,7 @@
+# Instructions
+
+Count the frequency of letters in texts using parallel computation.
+
+Parallelism is about doing things in parallel that can also be done sequentially.
+A common example is counting the frequency of letters.
+Employ parallelism to calculate the total frequency of each letter in a list of texts.

exercises/practice/parallel-letter-frequency/.meta/config.json

@@ -0,0 +1,15 @@
+{
+  "authors": ["kmarker1101"],
+  "files": {
+    "solution": [
+      "parallel-letter-frequency.el"
+    ],
+    "test": [
+      "parallel-letter-frequency-test.el"
+    ],
+    "example": [
+      ".meta/example.el"
+    ]
+  },
+  "blurb": "Count the frequency of letters in texts using parallel computation."
+}

exercises/practice/parallel-letter-frequency/.meta/example.el

@@ -0,0 +1,48 @@
+;;; parallel-letter-frequency.el --- Parallel Letter Frequency (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+(defun count-frequencies (text)
+  "Count the frequency of each letter in TEXT."
+  (let ((freqs (make-hash-table :test 'equal)))
+    (dolist (char (string-to-list (downcase text)))
+      (when (string-match-p "[[:alpha:]]" (char-to-string char))  ; Check if char is a Unicode letter
+        (puthash char (1+ (gethash char freqs 0)) freqs)))
+    freqs))
+
+(defun combine-frequencies (freqs-list)
+  "Combine a list of frequency hash tables into a single hash table."
+  (let ((combined-freqs (make-hash-table :test 'equal)))
+    (dolist (freqs freqs-list)
+      (maphash (lambda (key value)
+                 (puthash key (+ value (gethash key combined-freqs 0)) combined-freqs))
+               freqs))
+    combined-freqs))
+
+(defun calculate-frequencies (texts)
+  "Calculate letter frequencies for each string in TEXTS using threads."
+  (let ((threads (mapcar (lambda (text)
+                           (make-thread
+                            (lambda ()
+                              (count-frequencies text))))
+                         texts))
+        result
+        freqs-list)
+    ;; Wait for all threads to complete and collect their results
+    (dolist (thread threads)
+      (thread-join thread)
+      (push (thread-join thread) freqs-list))
+    ;; Combine the frequencies
+    (let ((combined-freqs (combine-frequencies freqs-list)))
+      (maphash (lambda (key value)
+                 (push (list (char-to-string key) value) result))
+               combined-freqs)
+      (setq result (sort result (lambda (a b) (string< (car a) (car b)))))
+      (setq result (apply 'append result))
+      result)))
+
+
+(provide 'parallel-letter-frequency)
+;;; parallel-letter-frequency.el ends here

exercises/practice/parallel-letter-frequency/.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.
+
+[c054d642-c1fa-4234-8007-9339f2337886]
+description = "no texts"
+
+[818031be-49dc-4675-b2f9-c4047f638a2a]
+description = "one text with one letter"
+
+[c0b81d1b-940d-4cea-9f49-8445c69c17ae]
+description = "one text with multiple letters"
+
+[708ff1e0-f14a-43fd-adb5-e76750dcf108]
+description = "two texts with one letter"
+
+[1b5c28bb-4619-4c9d-8db9-a4bb9c3bdca0]
+description = "two texts with multiple letters"
+
+[6366e2b8-b84c-4334-a047-03a00a656d63]
+description = "ignore letter casing"
+
+[92ebcbb0-9181-4421-a784-f6f5aa79f75b]
+description = "ignore whitespace"
+
+[bc5f4203-00ce-4acc-a5fa-f7b865376fd9]
+description = "ignore punctuation"
+
+[68032b8b-346b-4389-a380-e397618f6831]
+description = "ignore numbers"
+
+[aa9f97ac-3961-4af1-88e7-6efed1bfddfd]
+description = "Unicode letters"
+
+[7b1da046-701b-41fc-813e-dcfb5ee51813]
+description = "combination of lower- and uppercase letters, punctuation and white space"
+
+[4727f020-df62-4dcf-99b2-a6e58319cb4f]
+description = "large texts"
+
+[adf8e57b-8e54-4483-b6b8-8b32c115884c]
+description = "many small texts"