adventofcode/2018/day24/army.go

package main

import (
	"fmt"
	"strings"
)

const (
	ArmyTypeImmune = 1 << iota
	ArmyTypeInfection
)

type Army struct {
	id          int
	tp          int
	units       int
	hp          int
	immunities  []string
	weaknesses  []string
	damageType  string
	strength    int
	init        int
	target      *Army
	targettedBy *Army
}

func NewArmy(inp string, tp, id int) *Army {
	a := new(Army)
	a.tp = tp
	a.id = id

	// Pull the parenthetical out, if one is there
	var prnth, other string
	var inPrnth bool
	var ptsOfOther int
	for _, v := range strings.Fields(inp) {
		if len(v) > 0 && v[len(v)-1] == ')' {
			prnth = prnth + " " + v
			inPrnth = false
			continue
		} else if len(v) > 0 && v[0] == '(' {
			inPrnth = true
			prnth = v
			continue
		}
		if inPrnth {
			prnth = prnth + " " + v
		} else {
			if len(other) > 0 {
				other = other + " "
			}
			other = other + v
			ptsOfOther++
		}
	}
	_, err := fmt.Sscanf(other, "%d units each with %d hit points with an attack that does %d %s damage at initiative %d", &a.units, &a.hp, &a.strength, &a.damageType, &a.init)
	if err != nil {
		panic(err)
	}
	// Now parse out immunities and weaknesses
	if len(prnth) > 3 {
		prnth = prnth[1 : len(prnth)-1]
		var inImmune bool
		for _, v := range strings.Fields(prnth) {
			if v == "immune" {
				inImmune = true
				continue
			} else if v == "weak" {
				inImmune = false
				continue
			}
			if v == "to" {
				continue
			}
			if v[len(v)-1] == ';' || v[len(v)-1] == ',' {
				v = v[:len(v)-1]
			}
			if inImmune {
				a.immunities = append(a.immunities, v)
			} else {
				a.weaknesses = append(a.weaknesses, v)
			}
		}
	}
	return a
}

func (a *Army) IsImmuneTo(val string) bool {
	for _, v := range a.immunities {
		if v == val {
			return true
		}
	}
	return false
}

func (a *Army) IsWeakTo(val string) bool {
	for _, v := range a.weaknesses {
		if v == val {
			return true
		}
	}
	return false
}

func (a *Army) Power() int {
	return a.units * a.strength
}

func (a *Army) FindTarget(group []*Army) {
	var tgt *Army
	var tgtDmg int
	for _, v := range group {
		if v.targettedBy != nil {
			continue
		}
		wrkDmg := a.CalculateDamage(v)
		if tgt == nil || wrkDmg > tgtDmg {
			tgt = v
			tgtDmg = wrkDmg
		} else if wrkDmg == tgtDmg {
			if v.Power() > tgt.Power() {
				tgt = v
				tgtDmg = wrkDmg
			} else if v.Power() == tgt.Power() {
				if v.init > tgt.init {
					tgt = v
					tgtDmg = wrkDmg
				}
			}
		}
		if Debug {
			var tpTxt string
			if a.tp == ArmyTypeImmune {
				tpTxt = "Immune System"
			} else {
				tpTxt = "Infection"
			}
			fmt.Printf("%s group %d would deal defending group %d %d damage\n", tpTxt, a.id, tgt.id, tgtDmg)
		}
	}
	if tgt != nil {
		a.target = tgt
		tgt.targettedBy = a
	}
}

func (a *Army) CalculateDamage(b *Army) int {
	if b.IsWeakTo(a.damageType) {
		return a.Power() * 2
	} else if b.IsImmuneTo(a.damageType) {
		return 0
	}
	return a.Power()
}

func (a *Army) Damage(b *Army) int {
	var unitsDefeated int
	dmg := a.CalculateDamage(b)
	for dmg > 0 {
		dmg -= b.hp
		if dmg > 0 && b.units > 0 {
			b.units--
			unitsDefeated++
		}
	}
	b.targettedBy = nil
	return unitsDefeated
}

func (a *Army) Fight() {
	if a.target != nil {
		var tpTxt string
		if a.tp == ArmyTypeImmune {
			tpTxt = "Immune System"
		} else if a.tp == ArmyTypeInfection {
			tpTxt = "Infection"
		}
		dmg := a.Damage(a.target)
		if Debug {
			fmt.Printf("%s group %d attacks defending group %d, killing %d units\n", tpTxt, a.id, a.target.id, dmg)
		}
	}
}

func (a Army) String() string {
	ret := fmt.Sprintf("%d units each with %d hit points ", a.units, a.hp)
	if len(a.weaknesses) > 0 {
		ret = ret + fmt.Sprintf("(weaknesses: %s) ", a.weaknesses)
	}
	if len(a.immunities) > 0 {
		ret = ret + fmt.Sprintf("(immunities: %s) ", a.immunities)
	}
	ret = ret + fmt.Sprintf("with an attack that does %d %s damage at initiative %d\n",
		a.strength, a.damageType, a.init,
	)
	return ret
}

// Army Sorting
type ByPower []*Army

func (b ByPower) Len() int      { return len(b) }
func (b ByPower) Swap(i, j int) { b[i], b[j] = b[j], b[i] }
func (b ByPower) Less(i, j int) bool {
	if b[i].Power() == b[j].Power() {
		return b[i].init < b[j].init
	}
	return b[i].Power() < b[j].Power()
}