Add knapsack exercise (#107)

config.json

@@ -282,6 +282,14 @@
         "prerequisites": [],
         "difficulty": 5
       },
+      {
+        "slug": "knapsack",
+        "name": "Knapsack",
+        "uuid": "92dc3c46-5753-4726-88e0-54f93751c5bf",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6
+      },
       {
         "slug": "matching-brackets",
         "name": "Matching Brackets",

exercises/practice/knapsack/.docs/instructions.md

@@ -0,0 +1,25 @@
+# Instructions
+
+Your task is to determine which items to take so that the total value of his selection is maximized, taking into account the knapsack's carrying capacity.
+
+Items will be represented as a list of items.
+Each item will have a weight and value.
+All values given will be strictly positive.
+Bob can take only one of each item.
+
+For example:
+
+```text
+Items: [
+  { "weight": 5, "value": 10 },
+  { "weight": 4, "value": 40 },
+  { "weight": 6, "value": 30 },
+  { "weight": 4, "value": 50 }
+]
+
+Knapsack Maximum Weight: 10
+```
+
+For the above, the first item has weight 5 and value 10, the second item has weight 4 and value 40, and so on.
+In this example, Bob should take the second and fourth item to maximize his value, which, in this case, is 90.
+He cannot get more than 90 as his knapsack has a weight limit of 10.

exercises/practice/knapsack/.docs/introduction.md

@@ -0,0 +1,8 @@
+# Introduction
+
+Bob is a thief.
+After months of careful planning, he finally manages to crack the security systems of a fancy store.
+
+In front of him are many items, each with a value and weight.
+Bob would gladly take all of the items, but his knapsack can only hold so much weight.
+Bob has to carefully consider which items to take so that the total value of his selection is maximized.

exercises/practice/knapsack/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "knapsack.s"
+    ],
+    "test": [
+      "knapsack_test.c"
+    ],
+    "example": [
+      ".meta/example.s"
+    ]
+  },
+  "blurb": "Given a knapsack that can only carry a certain weight, determine which items to put in the knapsack in order to maximize their combined value.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Knapsack_problem"
+}

exercises/practice/knapsack/.meta/example.s

@@ -0,0 +1,49 @@
+.text
+.globl maximum_value
+
+/* extern uint32_t maximum_value(uint32_t maximum_weight, const item_t *items, size_t item_count); */
+maximum_value:
+        lsl     x2, x2, #3              /* number of bytes occupied by items */
+        add     x2, x1, x2              /* end of items */
+        lsl     x0, x0, #2
+        add     x3, x0, #16
+        and     x3, x3, #-16            /* number of bytes occupied by table, with (maximum_weight+1) uint32_t values, rounded up to a multiple of 16 */
+        mov     x4, sp
+        sub     sp, sp, x3
+        mov     x5, sp
+
+.clear:
+        stp     xzr, xzr, [x4, #-16]!   /* fill table with 0 */
+        cmp     x4, x5
+        bne     .clear
+
+.next_item:
+        cmp     x1, x2
+        beq     .report
+
+        ldr     w9, [x1], #4            /* load item weight, post-increment */
+        ldr     w10, [x1], #4           /* load item value, post-increment */
+        lsl     x9, x9, 2
+        mov     x7, x0
+        subs    x11, x7, x9
+        blt     .next_item
+
+.loop:
+        ldr     w12, [sp, x11]
+        add     w12, w12, w10           /* table value plus item value */
+        ldr     w13, [sp, x7]
+        cmp     w13, w12
+        bhs     .skip                   /* unsigned >= */  
+
+        str     w12, [sp, x7]           /* update table value */
+
+.skip:
+        cbz     x11, .next_item
+        sub     x7, x7, #4
+        sub     x11, x11, #4
+        b       .loop
+
+.report:
+        ldr     w0, [sp, x0]
+        add     sp, sp, x3
+        ret

exercises/practice/knapsack/.meta/tests.toml

@@ -0,0 +1,36 @@
+# 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.
+
+[a4d7d2f0-ad8a-460c-86f3-88ba709d41a7]
+description = "no items"
+include = false
+
+[3993a824-c20e-493d-b3c9-ee8a7753ee59]
+description = "no items"
+reimplements = "a4d7d2f0-ad8a-460c-86f3-88ba709d41a7"
+
+[1d39e98c-6249-4a8b-912f-87cb12e506b0]
+description = "one item, too heavy"
+
+[833ea310-6323-44f2-9d27-a278740ffbd8]
+description = "five items (cannot be greedy by weight)"
+
+[277cdc52-f835-4c7d-872b-bff17bab2456]
+description = "five items (cannot be greedy by value)"
+
+[81d8e679-442b-4f7a-8a59-7278083916c9]
+description = "example knapsack"
+
+[f23a2449-d67c-4c26-bf3e-cde020f27ecc]
+description = "8 items"
+
+[7c682ae9-c385-4241-a197-d2fa02c81a11]
+description = "15 items"

exercises/practice/knapsack/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/knapsack/knapsack.s

@@ -0,0 +1,5 @@
+.text
+.globl maximum_value
+
+maximum_value:
+    ret

exercises/practice/knapsack/knapsack_test.c

@@ -0,0 +1,71 @@
+#include "vendor/unity.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+typedef struct {
+    uint32_t weight;
+    uint32_t value;
+} item_t;
+
+extern uint32_t maximum_value(uint32_t maximum_weight, const item_t *items, size_t item_count);
+
+void setUp(void) {
+}
+
+void tearDown(void) {
+}
+
+void test_no_items(void) {
+    TEST_ASSERT_EQUAL_UINT(0, maximum_value(100, NULL, 0));
+}
+
+void test_one_item_too_heavy(void) {
+    TEST_IGNORE();
+    const item_t items[] = {{100, 1}};
+    TEST_ASSERT_EQUAL_UINT(0, maximum_value(10, items, ARRAY_SIZE(items)));
+}
+
+void test_five_items_cannot_be_greedy_by_weight(void) {
+    TEST_IGNORE();
+    const item_t items[] = {{2, 5}, {2, 5}, {2, 5}, {2, 5}, {10, 21}};
+    TEST_ASSERT_EQUAL_UINT(21, maximum_value(10, items, ARRAY_SIZE(items)));
+}
+
+void test_five_items_cannot_be_greedy_by_value(void) {
+    TEST_IGNORE();
+    const item_t items[] = {{2, 20}, {2, 20}, {2, 20}, {2, 20}, {10, 50}};
+    TEST_ASSERT_EQUAL_UINT(80, maximum_value(10, items, ARRAY_SIZE(items)));
+}
+
+void test_example_knapsack(void) {
+    TEST_IGNORE();
+    const item_t items[] = {{5, 10}, {4, 40}, {6, 30}, {4, 50}};
+    TEST_ASSERT_EQUAL_UINT(90, maximum_value(10, items, ARRAY_SIZE(items)));
+}
+
+void test_8_items(void) {
+    TEST_IGNORE();
+    const item_t items[] = {{25, 350}, {35, 400}, {45, 450}, {5, 20}, {25, 70}, {3, 8}, {2, 5}, {2, 5}};
+    TEST_ASSERT_EQUAL_UINT(900, maximum_value(104, items, ARRAY_SIZE(items)));
+}
+
+void test_15_items(void) {
+    TEST_IGNORE();
+    const item_t items[] = {{70, 135}, {73, 139}, {77, 149}, {80, 150}, {82, 156}, {87, 163}, {90, 173}, {94, 184}, {98, 192}, {106, 201}, {110, 210}, {113, 214}, {115, 221}, {118, 229}, {120, 240}};
+    TEST_ASSERT_EQUAL_UINT(1458, maximum_value(750, items, ARRAY_SIZE(items)));
+}
+
+int main(void) {
+    UNITY_BEGIN();
+    RUN_TEST(test_no_items);
+    RUN_TEST(test_one_item_too_heavy);
+    RUN_TEST(test_five_items_cannot_be_greedy_by_weight);
+    RUN_TEST(test_five_items_cannot_be_greedy_by_value);
+    RUN_TEST(test_example_knapsack);
+    RUN_TEST(test_8_items);
+    RUN_TEST(test_15_items);
+    return UNITY_END();
+}