river_crossing.go

package main

import (
	"fmt"
	"math/rand"
	"strings"
	"time"
)

type Player struct {
	Location int
	Speed    int
}

func main() {
	success := play("****~~*~~**~*~~*~*~*~*")
	fmt.Println(success)

	success2 := play("*****~~~*")
	fmt.Println(success2)
}

func play(River string) bool {
	player := Player{0, 0}

	waterLength := 0

	elements := strings.Split(River, "")

	for i, element := range elements {
		player.Location = i

		// change momentum if on a stepping stone.
		if element == "*" {
			player.Speed = player.Speed + speedDelta()
		}

		waterLength = trackJumpLength(waterLength, element)

		// track progress
		fmt.Println(player.Speed)
		fmt.Println(element)
		fmt.Println()

		if player.Speed < waterLength && element == "~" {
			return false
		}
	}
	return true
}

// returns random speed change from -1..1
func speedDelta() int {
	s := rand.NewSource(time.Now().UnixNano())
	r := rand.New(s)
	speedDelta := r.Intn(2)
	if r.Intn(2) == 1 {
		speedDelta = speedDelta * -1
	}

	return speedDelta
}

// calculates the accrued length of the river jump
func trackJumpLength(waterLength int, element string) int {
	if element == "~" {
		return waterLength + 1
	} else {
		return 0
	}
}