What kind of triangle? – Python Exercise with Solution

Decide what kind of triangle three lengths make.

What to build

A program in which one check must come before all the others.

Requirements

Print invalid if the three lengths cannot make a triangle.
Otherwise, print equilateral if all three are equal.
Otherwise, print isosceles if any two are equal.
Otherwise, print scalene.

Input

Three lines, each with one whole number.

Output

One word.

Constraints

Each length is from 1 to 1000.

Example

Input:

3
4
5

Output:

scalene

Why it works

If the longest side is at least as long as the other two together, the sides cannot meet, so that test has to come first. The equal-sides tests run from the most specific to the least.

Examples

Example 1 · Input

3
4
5

Expected output

scalene

Example 2 · Input

2
2
2

Expected output

equilateral

Prompts inside input() are ignored when checking, so input("n: ") is fine.

Hints

Hint 1

Check first whether a triangle is possible at all.

Hint 2

Three sides make a triangle only if each pair adds up to more than the third.

Hint 3

Test all three equal before testing any two equal.

Solution

Show one correct solution (try it yourself first)

a = int(input())
b = int(input())
c = int(input())
if a + b <= c or a + c <= b or b + c <= a:
    print("invalid")
elif a == b and b == c:
    print("equilateral")
elif a == b or b == c or a == c:
    print("isosceles")
else:
    print("scalene")

Lesson: Decisions with if →