2021 Day 18 Complete

2021/day18/main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"math"
 
 	h "git.bullercodeworks.com/brian/adventofcode/helpers"
 )
@@ -11,25 +12,34 @@ func main() {
 
 	var build *SNum
 	for i := range inp {
-		wrk, _ := ParseSNum(inp[i])
+		wrk := ParseSNum(inp[i])
 		if build == nil {
 			build = wrk
 		} else {
 			build = build.add(wrk)
 		}
 	}
-	fmt.Println(build)
-	v := build.needsExplode(0)
-	fmt.Println("Needs Explode:", v)
-	v.explode()
-	fmt.Println(build)
+	fmt.Println()
+	fmt.Println("# Part 1")
+	fmt.Println("Magnitude:", build.magnitude())
+	fmt.Println()
+	fmt.Println("# Part 2")
+	highest := h.MIN_INT
+	for i := 0; i < len(inp)-1; i++ {
+		for j := i + 1; j < len(inp); j++ {
+			w1 := ParseSNum(inp[i]).add(ParseSNum(inp[j]))
+			w2 := ParseSNum(inp[j]).add(ParseSNum(inp[i]))
 
-	/*
-		full := inp[0]
-		for i := 1; i < len(inp); i++ {
-			full = fmt.Sprintf("[%s,%s]", full, inp[i])
+			m1, m2 := w1.magnitude(), w2.magnitude()
+			if m1 >= m2 && m1 > highest {
+				highest = m1
+			} else if m2 > highest {
+				highest = m2
+			}
 		}
-	*/
+	}
+	fmt.Println("Highest magnitude from 2:", highest)
+	//3225 is too low
 }
 
 type SNum struct {
@@ -38,16 +48,21 @@ type SNum struct {
 	value               int
 }
 
+func ParseSNum(inp string) *SNum {
+	s, _ := rParseSNum(inp)
+	return s
+}
+
 // ParseSNum returns an SNum and what's left of inp
 // after it was produced
-func ParseSNum(inp string) (*SNum, string) {
+func rParseSNum(inp string) (*SNum, string) {
 	// inp should always start with either a number or a '['
 	var rest string
 	s := SNum{}
 	if inp[0] == '[' {
 		s.regular = false
-		s.left, rest = ParseSNum(inp[1:])
-		s.right, rest = ParseSNum(rest[1:])
+		s.left, rest = rParseSNum(inp[1:])
+		s.right, rest = rParseSNum(rest[1:])
 		s.left.parent = &s
 		s.right.parent = &s
 		return &s, rest[1:]
@@ -66,13 +81,21 @@ func ParseSNum(inp string) (*SNum, string) {
 	return &s, rest
 }
 
+// When exploding or splitting, we need to find the leftmost pair that matches the condition
 func (s *SNum) needsExplode(depth int) *SNum {
-	if depth == 4 && !s.regular {
-		return s
-	}
 	if s.regular {
 		return nil
 	}
+	if depth >= 4 {
+		if !s.left.regular {
+			return s.left.needsExplode(depth + 1)
+		} else if !s.right.regular {
+			return s.right.needsExplode(depth + 1)
+		} else {
+			return s
+		}
+	}
+
 	if tst := s.left.needsExplode(depth + 1); tst != nil {
 		return tst
 	} else if tst := s.right.needsExplode(depth + 1); tst != nil {
@@ -85,34 +108,69 @@ func (s *SNum) explode() {
 	if s.parent == nil {
 		return
 	}
-	s.parent.addToRegularRightOf(s.right.value, s)
 	s.parent.addToRegularLeftOf(s.left.value, s)
+	s.parent.addToRegularRightOf(s.right.value, s)
+	// Replace s with a regular number that just equals 0
+	s.regular, s.value = true, 0
+	s.right, s.left = nil, nil
+}
+
+func (s *SNum) needsSplit() *SNum {
+	if s == nil || (s.regular && s.value >= 10) {
+		return s
+	}
+	if tst := s.left.needsSplit(); tst != nil {
+		return tst
+	} else if tst := s.right.needsSplit(); tst != nil {
+		return tst
+	}
+	return nil
+}
+
+func (s *SNum) split() {
+	if s.parent == nil {
+		return
+	}
+	l := int(math.Floor(float64(s.value) / 2))
+	r := int(math.Ceil(float64(s.value) / 2))
+	n := SNum{
+		parent: s.parent,
+		left: &SNum{
+			regular: true,
+			value:   int(l),
+		},
+		right: &SNum{
+			regular: true,
+			value:   int(r),
+		},
+	}
+	n.left.parent = &n
+	n.right.parent = &n
+	if s.parent.left == s {
+		s.parent.left = &n
+	} else if s.parent.right == s {
+		s.parent.right = &n
+	}
 }
 
 func (s *SNum) addToRegularLeftOf(v int, c *SNum) {
-	if s.right.regular {
-		s.right.value += v
-	} else {
-		if s.right != nil && s.right == c {
-			r := s.left.findRightmostRegular()
-			if r != nil {
-				r.value += v
-			}
-		} else if s.left != nil && s.left == c {
-			s.parent.addToRegularLeftOf(v, s)
-		}
+	if s == nil || v == 0 {
+		return
+	}
+	if s.right != nil && s.right == c {
+		s.left.addToRightmostRegular(v)
+	} else if s.left != nil && s.left == c {
+		s.parent.addToRegularLeftOf(v, s)
 	}
 }
 
 func (s *SNum) addToRegularRightOf(v int, c *SNum) {
-	if s.left.regular {
-		s.left.value += v
-	} else if s.left != nil && s.left == c {
-		l := s.right.findLeftmostRegular()
-		if l != nil {
-			l.value += v
-		}
-	} else if s.right != nil && s.right == c {
+	if s == nil || v == 0 {
+		return
+	}
+	if s.left == c {
+		s.right.addToLeftmostRegular(v)
+	} else if s.right == c {
 		s.parent.addToRegularRightOf(v, s)
 	}
 }
@@ -121,24 +179,49 @@ func (s *SNum) contains(n *SNum) bool {
 	return s == n || s.left.contains(n) || s.right.contains(n)
 }
 
-func (s *SNum) findRightmostRegular() *SNum {
+func (s *SNum) addToRightmostRegular(v int) {
 	if s.regular {
-		return s
+		s.value += v
+	} else if s.right != nil {
+		s.right.addToRightmostRegular(v)
 	}
-	return s.right.findRightmostRegular()
 }
-func (s *SNum) findLeftmostRegular() *SNum {
+func (s *SNum) addToLeftmostRegular(v int) {
 	if s.regular {
-		return s
+		s.value += v
+	} else if s.left != nil {
+		s.left.addToLeftmostRegular(v)
 	}
-	return s.left.findLeftmostRegular()
 }
 
 func (s *SNum) add(n *SNum) *SNum {
-	return &SNum{
+	wrk := SNum{
 		left:  s,
 		right: n,
 	}
+	s.parent = &wrk
+	n.parent = &wrk
+
+	changed := true
+	for changed {
+		changed = false
+		if v := wrk.needsExplode(0); v != nil {
+			v.explode()
+			changed = true
+		} else if v := wrk.needsSplit(); v != nil {
+			v.split()
+			changed = true
+		}
+	}
+
+	return &wrk
+}
+
+func (s *SNum) magnitude() int {
+	if s.regular {
+		return s.value
+	}
+	return s.left.magnitude()*3 + s.right.magnitude()*2
 }
 
 func (s SNum) String() string {

2021/day18/testinput2

@@ -0,0 +1,2 @@
+[[[[4,3],4],4],[7,[[8,4],9]]]
+[1,1]

2021/day18/testinput3

@@ -0,0 +1,10 @@
+[[[0,[5,8]],[[1,7],[9,6]]],[[4,[1,2]],[[1,4],2]]]
+[[[5,[2,8]],4],[5,[[9,9],0]]]
+[6,[[[6,2],[5,6]],[[7,6],[4,7]]]]
+[[[6,[0,7]],[0,9]],[4,[9,[9,0]]]]
+[[[7,[6,4]],[3,[1,3]]],[[[5,5],1],9]]
+[[6,[[7,3],[3,2]]],[[[3,8],[5,7]],4]]
+[[[[5,4],[7,7]],8],[[8,3],8]]
+[[9,3],[[9,9],[6,[4,9]]]]
+[[2,[[7,7],7]],[[5,8],[[9,3],[0,2]]]]
+[[[[5,2],5],[8,[3,7]]],[[5,[7,5]],[4,4]]]