Exercise · Interfaces · lesson 9 of 10

Exercise: total area

The Shape interface with the method Area() float64 and the types Rect and Circle that implement it are already declared. Write a function func totalArea(shapes []Shape) float64 that returns the sum of the areas of all shapes in the slice — of any type that implements Shape, not only Rect and Circle.

r := Rect{Width: 2, Height: 3}, sq := Rect{Width: 1, Height: 1}, then totalArea([]Shape{r, sq}) → 7
c := Circle{Radius: 1}, then totalArea([]Shape{c}) → 3.141592653589793
totalArea(nil) → 0

Constraints: the same shape may appear in the slice several times and counts each time; the slice may be empty or nil, and then the sum is 0; the result is compared with a tolerance of 1e-9.

Do not add extra imports unless the task says so explicitly.

area.go — go

go · 28 lines

package area

import "math"

type Shape interface {
	Area() float64
}

type Rect struct {
	Width, Height float64
}

type Circle struct {
	Radius float64
}

func (r Rect) Area() float64 {
	return r.Width * r.Height
}

func (c Circle) Area() float64 {
	return math.Pi * c.Radius * c.Radius
}

func totalArea(shapes []Shape) float64 {
	return -1
}

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