Add largest-series-product exercise (#122)

config.json

@@ -346,6 +346,14 @@
         "prerequisites": [],
         "difficulty": 5
       },
+      {
+        "slug": "largest-series-product",
+        "name": "Largest Series Product",
+        "uuid": "26f31fed-b645-454e-86d6-c9db6d637f96",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "luhn",
         "name": "Luhn",

exercises/practice/largest-series-product/.docs/instructions.md

@@ -0,0 +1,26 @@
+# Instructions
+
+Your task is to look for patterns in the long sequence of digits in the encrypted signal.
+
+The technique you're going to use here is called the largest series product.
+
+Let's define a few terms, first.
+
+- **input**: the sequence of digits that you need to analyze
+- **series**: a sequence of adjacent digits (those that are next to each other) that is contained within the input
+- **span**: how many digits long each series is
+- **product**: what you get when you multiply numbers together
+
+Let's work through an example, with the input `"63915"`.
+
+- To form a series, take adjacent digits in the original input.
+- If you are working with a span of `3`, there will be three possible series:
+  - `"639"`
+  - `"391"`
+  - `"915"`
+- Then we need to calculate the product of each series:
+  - The product of the series `"639"` is 162 (`6 × 3 × 9 = 162`)
+  - The product of the series `"391"` is 27 (`3 × 9 × 1 = 27`)
+  - The product of the series `"915"` is 45 (`9 × 1 × 5 = 45`)
+- 162 is bigger than both 27 and 45, so the largest series product of `"63915"` is from the series `"639"`.
+  So the answer is **162**.

exercises/practice/largest-series-product/.docs/introduction.md

@@ -0,0 +1,5 @@
+# Introduction
+
+You work for a government agency that has intercepted a series of encrypted communication signals from a group of bank robbers.
+The signals contain a long sequence of digits.
+Your team needs to use various digital signal processing techniques to analyze the signals and identify any patterns that may indicate the planning of a heist.

exercises/practice/largest-series-product/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "largest_series_product.s"
+    ],
+    "test": [
+      "largest_series_product_test.c"
+    ],
+    "example": [
+      ".meta/example.s"
+    ]
+  },
+  "blurb": "Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.",
+  "source": "A variation on Problem 8 at Project Euler",
+  "source_url": "https://projecteuler.net/problem=8"
+}

exercises/practice/largest-series-product/.meta/example.s

@@ -0,0 +1,65 @@
+.equ INVALID_CHARACTER, -1
+.equ NEGATIVE_SPAN, -2
+.equ INSUFFICIENT_DIGITS, -3
+
+.text
+.globl largest_product
+
+/* extern int64_t largest_product(int span, const char *digits); */
+largest_product:
+        mov     x2, x1                  /* input pointer */
+
+.scan:
+        ldrb    w3, [x2], #1            /* load byte, with post-increment */
+        cbz     w3, .check_length
+
+        sub     w3, w3, #'0'
+        cmp     w3, #10
+        blo     .scan                   /* unsigned < */
+
+        mov     x0, INVALID_CHARACTER
+        ret
+
+.check_length:
+        sub     x2, x2, #1              /* address of null terminator */
+
+        cmp     w0, wzr                 /* compare with zero */
+        blt     .negative_span
+
+        sub     x3, x2, x1              /* number of digits */
+        cmp     x3, x0
+        blt     .insufficient_digits
+
+        mov     x4, x0                  /* span */
+        mov     x0, xzr                 /* largest product */
+
+.series:
+        add     x5, x1, x4              /* end of series */
+        mov     x6, #1                  /* current product */
+        mov     x7, x1                  /* input pointer */
+
+.digit:
+        cmp     x7, x5
+        beq     .update_largest
+
+        ldrb    w8, [x7], #1            /* load digit */
+        sub     w8, w8, #'0'
+        mul     x6, x6, x8
+        b       .digit
+
+.update_largest:
+        cmp     x6, x0
+        csel    x0, x6, x0, hi
+        cmp     x7, x2
+        add     x1, x1, #1              /* start of next series */
+        bne     .series
+
+        ret
+
+.negative_span:
+        mov     x0, NEGATIVE_SPAN
+        ret
+
+.insufficient_digits:
+        mov     x0, INSUFFICIENT_DIGITS
+        ret

exercises/practice/largest-series-product/.meta/tests.toml

@@ -0,0 +1,60 @@
+# 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.
+
+[7c82f8b7-e347-48ee-8a22-f672323324d4]
+description = "finds the largest product if span equals length"
+
+[88523f65-21ba-4458-a76a-b4aaf6e4cb5e]
+description = "can find the largest product of 2 with numbers in order"
+
+[f1376b48-1157-419d-92c2-1d7e36a70b8a]
+description = "can find the largest product of 2"
+
+[46356a67-7e02-489e-8fea-321c2fa7b4a4]
+description = "can find the largest product of 3 with numbers in order"
+
+[a2dcb54b-2b8f-4993-92dd-5ce56dece64a]
+description = "can find the largest product of 3"
+
+[673210a3-33cd-4708-940b-c482d7a88f9d]
+description = "can find the largest product of 5 with numbers in order"
+
+[02acd5a6-3bbf-46df-8282-8b313a80a7c9]
+description = "can get the largest product of a big number"
+
+[76dcc407-21e9-424c-a98e-609f269622b5]
+description = "reports zero if the only digits are zero"
+
+[6ef0df9f-52d4-4a5d-b210-f6fae5f20e19]
+description = "reports zero if all spans include zero"
+
+[5d81aaf7-4f67-4125-bf33-11493cc7eab7]
+description = "rejects span longer than string length"
+
+[06bc8b90-0c51-4c54-ac22-3ec3893a079e]
+description = "reports 1 for empty string and empty product (0 span)"
+
+[3ec0d92e-f2e2-4090-a380-70afee02f4c0]
+description = "reports 1 for nonempty string and empty product (0 span)"
+
+[6d96c691-4374-4404-80ee-2ea8f3613dd4]
+description = "rejects empty string and nonzero span"
+
+[7a38f2d6-3c35-45f6-8d6f-12e6e32d4d74]
+description = "rejects invalid character in digits"
+
+[5fe3c0e5-a945-49f2-b584-f0814b4dd1ef]
+description = "rejects negative span"
+include = false
+
+[c859f34a-9bfe-4897-9c2f-6d7f8598e7f0]
+description = "rejects negative span"
+reimplements = "5fe3c0e5-a945-49f2-b584-f0814b4dd1ef"

exercises/practice/largest-series-product/Makefile

@@ -0,0 +1,36 @@
+AS = aarch64-linux-gnu-as
+CC = aarch64-linux-gnu-gcc
+
+CFLAGS = -g -Wall -Wextra -pedantic -Werror
+LDFLAGS =
+
+ALL_LDFLAGS = -pie -Wl,--fatal-warnings
+
+ALL_CFLAGS = -std=c99 -fPIE $(CFLAGS)
+ALL_LDFLAGS += $(LDFLAGS)
+
+C_OBJS = $(patsubst %.c,%.o,$(wildcard *.c))
+AS_OBJS = $(patsubst %.s,%.o,$(wildcard *.s))
+ALL_OBJS = $(filter-out example.o,$(C_OBJS) $(AS_OBJS) vendor/unity.o)
+
+CC_CMD = $(CC) $(ALL_CFLAGS) -c -o $@ $<
+
+all: tests
+	qemu-aarch64 -L /usr/aarch64-linux-gnu ./$<
+
+tests: $(ALL_OBJS)
+	@$(CC) $(ALL_CFLAGS) $(ALL_LDFLAGS) -o $@ $(ALL_OBJS)
+
+%.o: %.s
+	@$(AS) -o $@ $<
+
+%.o: %.c
+	@$(CC_CMD)
+
+vendor/unity.o: vendor/unity.c vendor/unity.h vendor/unity_internals.h
+	@$(CC_CMD)
+
+clean:
+	@rm -f *.o vendor/*.o tests
+
+.PHONY: all clean

exercises/practice/largest-series-product/largest_series_product.s

@@ -0,0 +1,9 @@
+.equ INVALID_CHARACTER, -1
+.equ NEGATIVE_SPAN, -2
+.equ INSUFFICIENT_DIGITS, -3
+
+.text
+.globl largest_product
+
+largest_product:
+    ret

exercises/practice/largest-series-product/largest_series_product_test.c

@@ -0,0 +1,115 @@
+#include "vendor/unity.h"
+
+#include <stdint.h>
+
+#define INVALID_CHARACTER -1
+#define NEGATIVE_SPAN -2
+#define INSUFFICIENT_DIGITS -3
+
+extern int64_t largest_product(int span, const char *digits);
+
+void setUp(void) {
+}
+
+void tearDown(void) {
+}
+
+void test_finds_the_largest_product_if_span_equals_length(void) {
+    TEST_ASSERT_EQUAL_INT(18, largest_product(2, "29"));
+}
+
+void test_can_find_the_largest_product_of_2_with_numbers_in_order(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(72, largest_product(2, "0123456789"));
+}
+
+void test_can_find_the_largest_product_of_2(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(48, largest_product(2, "576802143"));
+}
+
+void test_can_find_the_largest_product_of_3_with_numbers_in_order(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(504, largest_product(3, "0123456789"));
+}
+
+void test_can_find_the_largest_product_of_3(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(270, largest_product(3, "1027839564"));
+}
+
+void test_can_find_the_largest_product_of_5_with_numbers_in_order(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(15120, largest_product(5, "0123456789"));
+}
+
+void test_can_get_the_largest_product_of_a_big_number(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(23520, largest_product(6, "73167176531330624919225119674426574742355349194934"));
+}
+
+void test_reports_zero_if_the_only_digits_are_zero(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(0, largest_product(2, "0000"));
+}
+
+void test_reports_zero_if_all_spans_include_zero(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(0, largest_product(3, "99099"));
+}
+
+void test_rejects_span_longer_than_string_length(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(INSUFFICIENT_DIGITS, largest_product(4, "123"));
+}
+
+void test_reports_1_for_empty_string_and_empty_product_0_span(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(1, largest_product(0, ""));
+}
+
+void test_reports_1_for_nonempty_string_and_empty_product_0_span(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(1, largest_product(0, "123"));
+}
+
+void test_rejects_empty_string_and_nonzero_span(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(INSUFFICIENT_DIGITS, largest_product(1, ""));
+}
+
+void test_rejects_invalid_character_in_digits(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(INVALID_CHARACTER, largest_product(2, "1234a5"));
+}
+
+void test_rejects_negative_span(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(NEGATIVE_SPAN, largest_product(-1, "12345"));
+}
+
+void test_large_span(void) {
+    TEST_IGNORE();
+    TEST_ASSERT_EQUAL_INT(131681894400, largest_product(17, "98765432123456789"));
+}
+
+int main(void) {
+    UNITY_BEGIN();
+    RUN_TEST(test_finds_the_largest_product_if_span_equals_length);
+    RUN_TEST(test_can_find_the_largest_product_of_2_with_numbers_in_order);
+    RUN_TEST(test_can_find_the_largest_product_of_2);
+    RUN_TEST(test_can_find_the_largest_product_of_3_with_numbers_in_order);
+    RUN_TEST(test_can_find_the_largest_product_of_3);
+    RUN_TEST(test_can_find_the_largest_product_of_5_with_numbers_in_order);
+    RUN_TEST(test_can_get_the_largest_product_of_a_big_number);
+    RUN_TEST(test_reports_zero_if_the_only_digits_are_zero);
+    RUN_TEST(test_reports_zero_if_all_spans_include_zero);
+    RUN_TEST(test_rejects_span_longer_than_string_length);
+    RUN_TEST(test_reports_1_for_empty_string_and_empty_product_0_span);
+    RUN_TEST(test_reports_1_for_nonempty_string_and_empty_product_0_span);
+    RUN_TEST(test_rejects_empty_string_and_nonzero_span);
+    RUN_TEST(test_rejects_invalid_character_in_digits);
+    RUN_TEST(test_rejects_negative_span);
+    RUN_TEST(test_large_span);
+    return UNITY_END();
+}