Working d8p2

.gitignore

@@ -22,3 +22,4 @@ go.work
 
 # Problem data
 input*.txt
+inputs/

day08/charpath.go

@@ -1,12 +1,12 @@
 package main
 
-import(
-	"fmt"
+import (
 	"bufio"
+	"fmt"
 	"os"
-	"sync"
+	"time"
 	"regexp"
-	"context"
+	"sync"
 )
 
 const LEFT = 'L'
@@ -17,7 +17,9 @@ type Nodes struct {
 	singleN  	[]int32
 	leftN    	[]int32
 	rightN   	[]int32
+	index    	int
 	steps    	uint64
+	allSteps 	[]int
 }
 
 func check(e error) {
@@ -31,12 +33,34 @@ func PrintAndWait(x ...any) {
 	fmt.Scanln()
 }
 
+// https://siongui.github.io/2017/06/03/go-find-lcm-by-gcd/
+// greatest common divisor (GCD) via Euclidean algorithm
+func GCD(a, b int) int {
+      for b != 0 {
+              t := b
+              b = a % b
+              a = t
+      }
+      return a
+}
+
+// find Least Common Multiple (LCM) via GCD
+func LCM(a, b int, integers ...int) int {
+      result := a * b / GCD(a, b)
+
+      for i := 0; i < len(integers); i++ {
+              result = LCM(result, integers[i])
+      }
+
+      return result
+}
+
 func (n *Nodes) toByteSingle(s string) {
 	// I've just received something like AAA
 	var temp int32
-    for i := 0; i < len(s); i++ {
+	for i := len(s) - 1; i >= 0; i-- {
 		a := int32(s[i])
-        temp +=  a << (i*8) 
+		temp += a << ((len(s) - 1 - i) * 8)
 	}
 	n.singleN = append(n.singleN, temp)
 }
@@ -44,26 +68,85 @@ func (n *Nodes) toByteSingle(s string) {
 func (n *Nodes) toByteDuet(s, r string) {
 	// I've just received something like AAA BBB
 	var tempL, tempR int32
-    for i := 0; i < len(s); i++ {
-        tempL += int32(s[i]) << (i*8)
-        tempR += int32(s[i]) << (i*8)
+	for i := len(s) - 1; i >= 0; i-- { 
+		tempL += int32(s[i]) << ((len(s) - 1 - i) * 8)
+		tempR += int32(r[i]) << ((len(s) - 1 - i) * 8)
 	}
 	n.leftN = append(n.leftN, tempL)
 	n.rightN = append(n.rightN, tempR)
 }
 
-func (n *Nodes) findNext(direction int32, index int, ctx context.Context) {
+func (n *Nodes) findNext(myN int32) int {
+	//var wg sync.WaitGroup
+	ind := 0
+	for i := 0; i < len(n.singleN); i++ {
+    	if myN^n.singleN[i] == 0 {
+        	n.mu.Lock()
+        	n.index = i
+        	n.mu.Unlock()
+        	ind = i
+        	break
+    	}
+	}
+	return ind
+}
 
+func (n *Nodes) findAll(ind int, sp []int, wg *sync.WaitGroup) {
+    index := 0
+    // We only go from the start
+	matching := n.rightN[sp[ind]] 
+	if n.commands[0]^LEFT == 0 {
+		matching = n.leftN[sp[ind]]
+	}
+	index = n.findNext(matching)
+	n.allSteps[ind]++
+	i := 0
+	for {
+		// Every step is in a single direction. For every step, we may need to
+		// scan len(n.singleN) elements.
+		// Circular loop
+		index = n.findNext(matching)
+		// Increment i after finding the match
+		i++
+		i = i % len(n.commands)
+		// By default, we will assume we are on the right
+		matching = n.rightN[index]
+		//PrintAndWait()
+		// If we are not, we are in the left
+		if n.commands[i]^LEFT == 0 {
+			matching = n.leftN[index]
+		}
+		n.allSteps[ind]++
+		// If we find XXZ, end
+		temp := matching & 255		
+		if  temp ^ 'Z' == 0 {
+    		break
+		}
+	}
+	//fmt.Printf("I started from %d, matched at %d, taking %d steps.\n", sp[ind], index, n.allSteps[ind] )
+	wg.Done()
+}
+
+func timer(name string) func() {
+	start := time.Now()
+	return func() {
+		fmt.Printf("%s took %v\n", name, time.Since(start))
+	}
 }
 
 func main() {
-	file, err := os.Open("./inputs/day08_test_input")
+	defer timer ("main")()
+	file, err := os.Open("./inputs/day08_input")
 	check(err)
 	defer file.Close()
 	// Struct with my node
 	n := Nodes{}
 	// Prepare the regex
 	repath := regexp.MustCompile("([A-Z]{3})")
+	// Build the END
+	var END = 'Z'
+	END += ('Z' << 8)
+	END += ('Z' << 16)
 
 	scanner := bufio.NewScanner(file)
 	scanner.Scan()
@@ -82,14 +165,69 @@ func main() {
 		n.toByteSingle(tempNodes[0])
 		n.toByteDuet(tempNodes[1], tempNodes[2])
 	}
-	ctx, cancel := context.WithCancel(context.Background())
-	defer cancel()
 	// We start from 0, we find the match
-	for i, j := 0, 0; ; i++ {
-    	// We do a circular loop
-    	i =  i % len(n.commands)
-    	// A function that has the context as an argument
-    	n.findNext(int32(i), j, ctx)  
-    	j++
+	// Let's start an infinite loop
+	// Circular index
+	i := 0
+	// We start from the AAA element
+	START := 'A'
+	START += ('A' << 8)
+	START += ('A' << 16)
+	matching := START
+	// Store where AAA is
+	n.findNext(matching) 
+	// By default, we will assume we are on the right
+	// If we are not, we are in the left
+	matching = n.rightN[n.index] 
+	if n.commands[i]^LEFT == 0 {
+		matching = n.leftN[n.index]
 	}
+	n.steps++
+	// Infinite loop
+	for {
+		// Every step is in a single direction. For every step, we may need to
+		// scan len(n.singleN) elements.
+		// Circular loop
+		n.findNext(matching)
+		// Increment i after finding the match
+		i++
+		i = i % len(n.commands)
+		// By default, we will assume we are on the right
+		matching = n.rightN[n.index]
+		//PrintAndWait()
+		// If we are not, we are in the left
+		if n.commands[i]^LEFT == 0 {
+			matching = n.leftN[n.index]
+		}
+		n.steps++
+		// If we find ZZZ, end
+		if matching^END == 0 {
+			break
+		}
+	}
+	fmt.Printf("\nSteps: %d\n", n.steps)
+	// Now, for the main event
+	// Let's get ready to rumble
+	startPoints := make([]int, 0)
+	for i := 0; i < len(n.singleN); i++ {
+    	// Lets remove all bytes except last 8
+    	temp := n.singleN[i] & 255
+    	if (temp ^ 'A') == 0 {
+        	startPoints = append(startPoints, i) 
+    	}
+	}
+	// Now, from the starting points, we should go and match until
+	// we find a path that ends in Z
+	n.allSteps = make([]int, len(startPoints))
+	var wg sync.WaitGroup
+	for i := 0; i < len(startPoints); i++ {
+    	wg.Add(1)
+    	go n.findAll(i, startPoints, &wg)
+	}
+	wg.Wait()
+	result := 1
+	for i := 0; i < len(n.allSteps); i++ {
+    	result = LCM(result, n.allSteps[i])
+	}
+	fmt.Printf("Steps: %d\n", result) 
 }