Merge pull request #35 from ikostan/exercism-sync/f7ebd665f8757e1e

[Sync Iteration] python/triangle/3

Author: ikostan

solutions/python/triangle/3/triangle.py

@@ -0,0 +1,52 @@
+"""Determine if a triangle is equilateral, isosceles, or scalene."""
+
+
+def equilateral(sides: list) -> bool:
+    """
+    An equilateral triangle has all three sides the same length.
+    """
+    if all_sides_positive(sides) and no_inequality_violation(sides):
+        return sides[0] == sides[1] == sides[2]
+    return False
+
+
+def isosceles(sides: list) -> bool:
+    """
+    An isosceles triangle has at least two sides the same length.
+    (It is sometimes specified as having exactly two sides the same length,
+    but for the purposes of this exercise we'll say at least two.)
+    """
+    if all_sides_positive(sides) and no_inequality_violation(sides):
+        return sides[0] == sides[1] or sides[1] == sides[2] or sides[0] == sides[2]
+    return False
+
+
+def scalene(sides: list) -> bool:
+    """
+    A scalene triangle has all sides of different lengths.
+    """
+    if all_sides_positive(sides) and no_inequality_violation(sides):
+        return sides[0] != sides[1] and sides[1] != sides[2] and sides[0] != sides[2]
+    return False
+
+
+def no_inequality_violation(sides: list) -> bool:
+    """
+    Let a, b, and c be sides of the triangle.
+    Then all three of the following expressions must be true:
+
+    a + b ≥ c
+    b + c ≥ a
+    a + c ≥ b
+    """
+    return (sides[0] + sides[1] >= sides[2] and
+            sides[0] + sides[2] >= sides[1] and
+            sides[2] + sides[1] >= sides[0])
+
+
+def all_sides_positive(sides: list) -> bool:
+    """
+    No zeroes or negative numbers allowed.
+    All triangles should have 3 sides.
+    """
+    return all(side > 0 for side in sides) and len(sides) == 3