Add run-length-encoding exercise (#416)

config.json

@@ -150,6 +150,14 @@
         ],
         "difficulty": 1
       },
+      {
+        "slug": "run-length-encoding",
+        "name": "Run Length Encoding",
+        "uuid": "71e5d918-6327-442a-98e8-3f9560b1ecd9",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
+      },
       {
         "slug": "isogram",
         "name": "Isogram",

exercises/practice/run-length-encoding/.docs/instructions.md

@@ -0,0 +1,20 @@
+# Instructions
+
+Implement run-length encoding and decoding.
+
+Run-length encoding (RLE) is a simple form of data compression, where runs (consecutive data elements) are replaced by just one data value and count.
+
+For example we can represent the original 53 characters with only 13.
+
+```text
+"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"  ->  "12WB12W3B24WB"
+```
+
+RLE allows the original data to be perfectly reconstructed from the compressed data, which makes it a lossless data compression.
+
+```text
+"AABCCCDEEEE"  ->  "2AB3CD4E"  ->  "AABCCCDEEEE"
+```
+
+For simplicity, you can assume that the unencoded string will only contain the letters A through Z (either lower or upper case) and whitespace.
+This way data to be encoded will never contain any numbers and numbers inside data to be decoded always represent the count for the following character.

exercises/practice/run-length-encoding/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "run_length_encoding.zig"
+    ],
+    "test": [
+      "test_run_length_encoding.zig"
+    ],
+    "example": [
+      ".meta/example.zig"
+    ]
+  },
+  "blurb": "Implement run-length encoding and decoding.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Run-length_encoding"
+}

exercises/practice/run-length-encoding/.meta/example.zig

@@ -0,0 +1,66 @@
+pub fn encode(buffer: []u8, string: []const u8) []u8 {
+    // We process the input string backwards,
+    // and reverse our output as our final step.
+
+    var inIndex: usize = string.len;
+    var outIndex: usize = 0;
+    var runLength: usize = 0;
+    while (inIndex > 0) {
+        inIndex -= 1;
+        const ch = string[inIndex];
+        runLength += 1;
+        if (inIndex > 0 and ch == string[inIndex - 1]) {
+            continue;
+        }
+
+        buffer[outIndex] = ch;
+        outIndex += 1;
+        if (runLength == 1) {
+            runLength = 0;
+            continue;
+        }
+
+        while (runLength > 0) {
+            const units: u8 = @intCast(runLength % 10);
+            buffer[outIndex] = '0' + units;
+            outIndex += 1;
+            runLength /= 10;
+        }
+    }
+
+    // Reverse buffer[0..outIndex]
+    var lowIndex: usize = 0;
+    var highIndex: usize = outIndex;
+    while (lowIndex + 1 < highIndex) {
+        highIndex -= 1;
+        const a = buffer[lowIndex];
+        const b = buffer[highIndex];
+        buffer[highIndex] = a;
+        buffer[lowIndex] = b;
+        lowIndex += 1;
+    }
+
+    return buffer[0..outIndex];
+}
+
+pub fn decode(buffer: []u8, string: []const u8) []u8 {
+    var inIndex: usize = 0;
+    var outIndex: usize = 0;
+    var runLength: usize = 0;
+    while (inIndex < string.len) {
+        const ch: u8 = string[inIndex];
+        inIndex += 1;
+        const units: u8 = ch -% '0';
+        if (units <= 9) {
+            runLength = runLength * 10 + units;
+            continue;
+        }
+
+        const endIndex = outIndex + @max(runLength, 1);
+        @memset(buffer[outIndex..endIndex], ch);
+        outIndex = endIndex;
+        runLength = 0;
+    }
+
+    return buffer[0..outIndex];
+}

exercises/practice/run-length-encoding/.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.
+
+[ad53b61b-6ffc-422f-81a6-61f7df92a231]
+description = "run-length encode a string -> empty string"
+
+[52012823-b7e6-4277-893c-5b96d42f82de]
+description = "run-length encode a string -> single characters only are encoded without count"
+
+[b7868492-7e3a-415f-8da3-d88f51f80409]
+description = "run-length encode a string -> string with no single characters"
+
+[859b822b-6e9f-44d6-9c46-6091ee6ae358]
+description = "run-length encode a string -> single characters mixed with repeated characters"
+
+[1b34de62-e152-47be-bc88-469746df63b3]
+description = "run-length encode a string -> multiple whitespace mixed in string"
+
+[abf176e2-3fbd-40ad-bb2f-2dd6d4df721a]
+description = "run-length encode a string -> lowercase characters"
+
+[7ec5c390-f03c-4acf-ac29-5f65861cdeb5]
+description = "run-length decode a string -> empty string"
+
+[ad23f455-1ac2-4b0e-87d0-b85b10696098]
+description = "run-length decode a string -> single characters only"
+
+[21e37583-5a20-4a0e-826c-3dee2c375f54]
+description = "run-length decode a string -> string with no single characters"
+
+[1389ad09-c3a8-4813-9324-99363fba429c]
+description = "run-length decode a string -> single characters with repeated characters"
+
+[3f8e3c51-6aca-4670-b86c-a213bf4706b0]
+description = "run-length decode a string -> multiple whitespace mixed in string"
+
+[29f721de-9aad-435f-ba37-7662df4fb551]
+description = "run-length decode a string -> lowercase string"
+
+[2a762efd-8695-4e04-b0d6-9736899fbc16]
+description = "encode and then decode -> encode followed by decode gives original string"

exercises/practice/run-length-encoding/run_length_encoding.zig

@@ -0,0 +1,11 @@
+pub fn encode(buffer: []u8, string: []const u8) []u8 {
+    _ = buffer;
+    _ = string;
+    @compileError("please implement the encode function");
+}
+
+pub fn decode(buffer: []u8, string: []const u8) []u8 {
+    _ = buffer;
+    _ = string;
+    @compileError("please implement the decode function");
+}

exercises/practice/run-length-encoding/test_run_length_encoding.zig

@@ -0,0 +1,79 @@
+const std = @import("std");
+const testing = std.testing;
+
+const run_length_encoding = @import("run_length_encoding.zig");
+
+fn testEncode(string: []const u8, expected: []const u8) !void {
+    const buffer_size = 80;
+    var buffer: [buffer_size]u8 = undefined;
+    const actual = run_length_encoding.encode(&buffer, string);
+    try testing.expectEqualStrings(expected, actual);
+}
+
+fn testDecode(string: []const u8, expected: []const u8) !void {
+    const buffer_size = 80;
+    var buffer: [buffer_size]u8 = undefined;
+    const actual = run_length_encoding.decode(&buffer, string);
+    try testing.expectEqualStrings(expected, actual);
+}
+
+fn testConsistency(string: []const u8, expected: []const u8) !void {
+    const buffer_size = 80;
+    var buffer1: [buffer_size]u8 = undefined;
+    var buffer2: [buffer_size]u8 = undefined;
+    const encoded = run_length_encoding.encode(&buffer1, string);
+    const actual = run_length_encoding.decode(&buffer2, encoded);
+    try testing.expectEqualStrings(expected, actual);
+}
+
+test "run-length encode a string-empty string" {
+    try testEncode("", "");
+}
+
+test "run-length encode a string-single characters only are encoded without count" {
+    try testEncode("XYZ", "XYZ");
+}
+
+test "run-length encode a string-string with no single characters" {
+    try testEncode("AABBBCCCC", "2A3B4C");
+}
+
+test "run-length encode a string-single characters mixed with repeated characters" {
+    try testEncode("WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB", "12WB12W3B24WB");
+}
+
+test "run-length encode a string-multiple whitespace mixed in string" {
+    try testEncode("  hsqq qww  ", "2 hs2q q2w2 ");
+}
+
+test "run-length encode a string-lowercase characters" {
+    try testEncode("aabbbcccc", "2a3b4c");
+}
+
+test "run-length decode a string-empty string" {
+    try testDecode("", "");
+}
+
+test "run-length decode a string-single characters only" {
+    try testDecode("XYZ", "XYZ");
+}
+
+test "run-length decode a string-string with no single characters" {
+    try testDecode("2A3B4C", "AABBBCCCC");
+}
+
+test "run-length decode a string-single characters with repeated characters" {
+    try testDecode("12WB12W3B24WB", "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB");
+}
+
+test "run-length decode a string-multiple whitespace mixed in string" {
+    try testDecode("2 hs2q q2w2 ", "  hsqq qww  ");
+}
+
+test "run-length decode a string-lowercase string" {
+    try testDecode("2a3b4c", "aabbbcccc");
+}
+
+test "encode and then decode-encode followed by decode gives original string" {
+    try testConsistency("zzz ZZ  zZ", "zzz ZZ  zZ");
+}