2020-day14: bitwise nonsense but got there eventually... ~2500?

2020/day14/main.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"strings"
 
-	"github.com/alexchao26/advent-of-code-go/mathutil"
 	"github.com/alexchao26/advent-of-code-go/util"
 )
 
@@ -15,32 +14,114 @@ func main() {
 	flag.Parse()
 	fmt.Println("Running part", part)
 
+	var ans int
 	if part == 1 {
-		ans := part1(util.ReadFile("./input.txt"))
-		util.CopyToClipboard(fmt.Sprintf("%v", ans))
-		fmt.Println("Output:", ans)
+		ans = part1(util.ReadFile("./input.txt"))
 	} else {
-		ans := part2(util.ReadFile("./input.txt"))
-		util.CopyToClipboard(fmt.Sprintf("%v", ans))
-		fmt.Println("Output:", ans)
+		ans = part2(util.ReadFile("./input.txt"))
 	}
+	fmt.Println("Output:", ans)
 }
 
 func part1(input string) int {
-	parsed := parseInput(input)
-	_ = parsed
+	groups := parseGroups(input)
+	memory := map[int]int{}
+	for _, group := range groups {
+		for _, instruction := range group.instructions {
+			address, value := instruction[0], instruction[1]
+			// overwrite val w/ bit shifts and shit
+			for index, overwrite := range group.mask {
+				if overwrite == "1" {
+					// run bitwise or
+					value |= 1 << index
+				} else if overwrite == "0" {
+					// OR w/ a 1 -> 1; XOR w/ a 1 -> 0
+					value |= 1 << index
+					value ^= 1 << index
+				}
+			}
 
-	return 0
+			// set the overwritten value into memory
+			memory[address] = value
+		}
+	}
+
+	return getTotal(memory)
 }
 
 func part2(input string) int {
-	return 0
+	groups := parseGroups(input)
+	memory := map[int]int{}
+	for _, group := range groups {
+		for _, instruction := range group.instructions {
+			address, value := instruction[0], instruction[1]
+
+			var floatingIndices []int
+			for index, overwrite := range group.mask {
+				if overwrite == "1" {
+					address |= 1 << index
+				} else if overwrite == "X" {
+					floatingIndices = append(floatingIndices, index)
+				}
+			}
+
+			// ugly way to get all the permutations (with one extra) of all possible addresses
+			perms := []int{address}
+			for _, index := range floatingIndices {
+				for _, perm := range perms {
+					// for each existing permutation, get the permutation with this floating index
+					// flipped to a 1, and to a zero
+					with1 := perm | 1<<index  // OR with a shifted 1 -> 1
+					with0 := with1 ^ 1<<index // with1 XOR'ed with a shifted 1 -> 0
+					perms = append(perms, with1, with0)
+				}
+			}
+			// make writes to memory for each perm
+			for _, index := range perms {
+				memory[index] = value
+			}
+		}
+	}
+
+	return getTotal(memory)
 }
 
-func parseInput(input string) (ans []int) {
-	lines := strings.Split(input, "\n")
-	for _, l := range lines {
-		ans = append(ans, mathutil.StrToInt(l))
-	}
-	return ans
+// each grouping contains a mask at the start, then a pairs of memory addressed to values
+type group struct {
+	mask         map[int]string
+	instructions [][2]int // memory address, overwrite value
+}
+
+func parseGroups(input string) []*group {
+	var groups []*group
+
+	for _, line := range strings.Split(input, "\n") {
+		if strings.HasPrefix(line, "mask") {
+			// start a new group
+			newGroup := &group{mask: map[int]string{}}
+			groups = append(groups, newGroup)
+
+			var maskValue string
+			fmt.Sscanf(line, "mask = %s", &maskValue)
+
+			// iterate backwards so that keys in the mask map will correspond to powers of two
+			for i := len(maskValue) - 1; i >= 0; i-- {
+				newGroup.mask[len(maskValue)-i-1] = string(maskValue[i])
+			}
+		} else {
+			currentGroup := groups[len(groups)-1]
+			var index, val int
+			fmt.Sscanf(line, "mem[%d] = %d", &index, &val)
+			currentGroup.instructions = append(currentGroup.instructions, [2]int{index, val})
+		}
+	}
+	return groups
+}
+
+func getTotal(memory map[int]int) int {
+	var sum int
+	for _, v := range memory {
+		sum += v
+	}
+	return sum
 }

2020/day14/main_test.go

@@ -2,6 +2,8 @@ package main
 
 import (
 	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
 )
 
 func Test_part1(t *testing.T) {
@@ -10,7 +12,7 @@ func Test_part1(t *testing.T) {
 		input string
 		want  int
 	}{
-		// {"actual", util.ReadFile("input.txt"), ACTUAL_ANSWER},
+		{"actual", util.ReadFile("input.txt"), 14925946402938},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -21,13 +23,19 @@ func Test_part1(t *testing.T) {
 	}
 }
 
+var example = `mask = 000000000000000000000000000000X1001X
+mem[42] = 100
+mask = 00000000000000000000000000000000X0XX
+mem[26] = 1`
+
 func Test_part2(t *testing.T) {
 	tests := []struct {
 		name  string
 		input string
 		want  int
 	}{
-		// {"actual", util.ReadFile("input.txt"), ACTUAL_ANSWER},
+		{"example", example, 208},
+		{"actual", util.ReadFile("input.txt"), 3706820676200},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {