adventofcode/2022/day21/main.go

package main

import (
	"flag"
	"fmt"
	"log"

	h "git.bullercodeworks.com/brian/adventofcode/helpers"
)

type Monkey struct {
	name         string
	yelled       bool
	value        int
	m1, m2       *Monkey
	op           string
	name1, name2 string
}

var monkeys map[string]*Monkey
var verbose bool
var humanval int

func main() {
	partOne := flag.Bool("1", false, "run exercise part1, (default: part2)")
	verboseFlag := flag.Bool("v", false, "verbose: print extra info")
	humanFlag := flag.Int("h", -1, "set value of \"humn\" monkey, return delta")
	flag.Parse()
	verbose = *verboseFlag
	humanval = *humanFlag
	lines := h.StdinToStringSlice()
	parse(lines)

	var result int
	if *partOne {
		vprint("Running Part 1")
		result = part1(lines)
	} else {
		vprint("Running Part 2")
		result = part2(lines)
	}
	fmt.Println(result)
}

func part1(lines []string) int {
	return listenCached(monkeys["root"])
}

func part2(lines []string) int {
	root := monkeys["root"]
	delta := Monkey{name: "delta", m1: root.m1, m2: root.m2, name1: root.name1, name2: root.name2, op: "-"}
	if humanval != -1 {
		human := monkeys["humn"]
		human.yelled = true
		human.value = humanval
		return listenCached(&delta)
	}
	// We find the value of human making delta == 0 by dichotomy
	return humanZeroing(&delta)
}

func parse(lines []string) {
	var name, name1, op, name2 string
	var num int
	monkeys = make(map[string]*Monkey, 0)
	// 1st pass, gather names
	for _, line := range lines {
		if n, _ := fmt.Sscanf(line, "%s %d", &name, &num); n == 2 {
			m := Monkey{name: name[:len(name)-1], value: num, yelled: true}
			monkeys[name[:len(name)-1]] = &m
		} else if n, _ = fmt.Sscanf(line, "%s %s %s %s", &name, &name1, &op, &name2); n == 4 {
			m := Monkey{name: name[:len(name)-1], op: op, name1: name1, name2: name2}
			monkeys[name[:len(name)-1]] = &m
		} else {
			log.Fatalf("Parse error: %s\n", line)
		}
	}
	// 2nd pass, fill the sub-monkey fields
	for _, m := range monkeys {
		if !m.yelled {
			m.m1 = monkeys[m.name1]
			m.m2 = monkeys[m.name2]
		}
	}
}

// Resolve and cache result. Faster but cannot be reused
func listenCached(m *Monkey) int {
	if m.yelled {
		return m.value
	}
	n1 := listenCached(m.m1)
	n2 := listenCached(m.m2)
	m.yelled = true
	switch m.op {
	case "+":
		m.value = n1 + n2
	case "-":
		m.value = n1 - n2
	case "*":
		m.value = n1 * n2
	case "/":
		m.value = n1 / n2
	}
	return m.value
}

func listen(m *Monkey) int {
	if m.yelled {
		return m.value
	}
	n1 := listen(m.m1)
	n2 := listen(m.m2)
	switch m.op {
	case "+":
		return n1 + n2
	case "-":
		return n1 - n2
	case "*":
		return n1 * n2
	case "/":
		return n1 / n2
	}
	return 0
}
func listenFor(d, h *Monkey, value int) int {
	h.value = value
	return listen(d)
}

func humanZeroing(delta *Monkey) int {
	human := monkeys["humn"]
	human.yelled = true
	h1 := 0
	h2 := 1000
	for {
		d1 := listenFor(delta, human, h1)
		d2 := listenFor(delta, human, h2)
		d2d1 := d2 - d1
		vprintf("%d, %d --> %d, %d (diff: %d)\n", h1, h2, d1, d2, d2d1)
		if d1 == 0 {
			return humanSmallest(delta, human, h1)
		} // found
		if d2 == 0 {
			return humanSmallest(delta, human, h2)
		} // found
		if d2d1 == 0 {
			log.Fatalf("d2 == d1\n")
		}
		// Linear regresion on h to minimize d
		if absInt(d1) < absInt(d2) {
			// h1 was closest to the goal: interpolate from it
			h := h1 - (d1*(h2-h1))/d2d1
			vprintf("==> h = %d (h1=%d + %d)\n", h, h1, -(d1*(h2-h1))/d2d1)
			h2 = h
		} else {
			// h2 was closest to the goal: interpolate from it
			h := h2 - (d2*(h1-h2))/(-d2d1)
			vprintf("==> h = %d (h2=%d + %d)\n", h, h2, -(d2*(h1-h2))/(-d2d1))
			h1 = h
		}
	}
}

func humanSmallest(delta, human *Monkey, hval int) int {
	h := hval
	for listenFor(delta, human, h-1) == 0 {
		h--
	}
	return h
}

func absInt(i int) int {
	if i < 0 {
		return -i
	}
	return i
}

func vprintf(f string, vals ...interface{}) {
	if !verbose {
		return
	}
	fmt.Printf(f, vals...)
}
func vprint(txt string) {
	if !verbose {
		return
	}
	fmt.Println(txt)
}