Go Track - Interest is Interesting: I can't seem to pass one last test

Programming Go
1

Hello! :wave:

I’m going through the Go track and this is the most fun I’ve had learning to code so far. But, I’m halted by a single test in the Interest is Interesting exercise: FAIL: TestYearsBeforeDesiredBalance/Result_balance_would_be_exactly_same_as_target: Want 2, got 3.

Now, I have checked my code, I have checked the community solutions, as far as I’m concerned it should just work™. Yet here I am. If any fresh pairs of eyes could take a look and tell me the error of my ways I’d be grateful.

Here is the code below:

package interest

const BelowZero, ToThousand, ToFiveThousand, AboveFiveThousand float64 = 3.213, 0.5, 1.621, 2.475

// InterestRate returns the interest rate for the provided balance.
func InterestRate(balance float64) float32 {
	if balance < 0 {
		return float32(BelowZero)
	} else if balance >= 0 && balance < 1000 {
		return float32(ToThousand)
	} else if balance >= 1000 && balance < 5000 {
		return float32(ToFiveThousand)
	} else {
		return float32(AboveFiveThousand)
	}
}

// Interest calculates the interest for the provided balance.
func Interest(balance float64) float64 {
	var interest float64
	if balance < 0 {
		interest = balance * (BelowZero / 100.0)
	} else if balance >= 0 && balance < 1000 {
		interest = balance * (ToThousand / 100.0)
	} else if balance >= 1000 && balance < 5000 {
		interest = balance * (ToFiveThousand / 100.0)
	} else {
		interest = balance * (AboveFiveThousand / 100.0)
	}
	return interest
}

// AnnualBalanceUpdate calculates the annual balance update, taking into account the interest rate.
func AnnualBalanceUpdate(balance float64) float64 {
	var newBalance float64
	if balance < 0 {
		newBalance = balance + Interest(balance)
	} else if balance >= 0 && balance < 1000 {
		newBalance = balance + Interest(balance)
	} else if balance >= 1000 && balance < 5000 {
		newBalance = balance + Interest(balance)
	} else {
		newBalance = balance + Interest(balance)
	}
	return newBalance
}

// YearsBeforeDesiredBalance calculates the minimum number of years required to reach the desired balance.
func YearsBeforeDesiredBalance(balance, targetBalance float64) int {
	years := 0
	for balance < targetBalance {
		balance = AnnualBalanceUpdate(balance)
		years++
	}
	return years
}

Cheers!

2

First of all, simplify your conditions. I’ll have a look into the error.

1 Like
3

For Interest and AnnualBalanceUpdate you should use your own functions and not define the decision logic again. Because of that, your solution currently uses the wrong type (float64 instead of float32), which results in different numbers.

2 Likes
4

Thanks for taking a look! I see the error in there now! Here’s the final version of the code:

package interest

// InterestRate returns the interest rate for the provided balance.
func InterestRate(balance float64) float32 {
	switch {
	case balance >= 5000:
		return 2.475
	case balance >= 1000:
		return 1.621
	case balance >= 0:
		return 0.5
	default:
		return 3.213
	}
}

// Interest calculates the interest for the provided balance.
func Interest(balance float64) float64 {
	return balance * float64(InterestRate(balance)/100)
}

// AnnualBalanceUpdate calculates the annual balance update, taking into account the interest rate.
func AnnualBalanceUpdate(balance float64) float64 {
	return balance + Interest(balance)
}

// YearsBeforeDesiredBalance calculates the minimum number of years required to reach the desired balance.
func YearsBeforeDesiredBalance(balance, targetBalance float64) int {
	years := 0
	for balance < targetBalance {
		balance = AnnualBalanceUpdate(balance)
		years++
	}
	return years
}

I really did miss the forest for the trees there. Like, I repeated the same function in every if statement because I was searching for where the problem was so gosh darn hard to make it pass that last test. Also, for some reason I had forgotten that a switch statement would return the value at the first chance, not go down the list.

2 Likes