Week 5: Object Oriented Programming 9. Classes and Inheritance Exercise: int set

Posted 2020-10-17 爱学英语的程序媛

class intSet(object):
    """An intSet is a set of integers
    The value is represented by a list of ints, self.vals.
    Each int in the set occurs in self.vals exactly once."""

    def __init__(self):
        """Create an empty set of integers"""
        self.vals = []

    def insert(self, e):
        """Assumes e is an integer and inserts e into self""" 
        if not e in self.vals:
            self.vals.append(e)

    def member(self, e):
        """Assumes e is an integer
           Returns True if e is in self, and False otherwise"""
        return e in self.vals

    def remove(self, e):
        """Assumes e is an integer and removes e from self
           Raises ValueError if e is not in self"""
        try:
            self.vals.remove(e)
        except:
            raise ValueError(str(e) + ‘ not found‘)

    def __str__(self):
        """Returns a string representation of self"""
        self.vals.sort()
        return ‘{‘ + ‘,‘.join([str(e) for e in self.vals]) + ‘}‘

Your task is to define the following two methods for the intSet class:

1. Define an intersect method that returns a new intSet containing elements that appear in both sets. In other words,

   s1.intersect(s2)

   would return a new intSet of integers that appear in both s1 and s2. Think carefully - what should happen if s1 and s2 have no elements in common?

2. Add the appropriate method(s) so that len(s) returns the number of elements in s.

   Hint: look through the Python docs to figure out what you‘ll need to solve this problem.

class intSet(object):
    """An intSet is a set of integers
    The value is represented by a list of ints, self.vals.
    Each int in the set occurs in self.vals exactly once."""

    def __init__(self):
        """Create an empty set of integers"""
        self.vals = []

    def insert(self, e):
        """Assumes e is an integer and inserts e into self""" 
        if not e in self.vals:
            self.vals.append(e)

    def member(self, e):
        """Assumes e is an integer
           Returns True if e is in self, and False otherwise"""
        return e in self.vals

    def remove(self, e):
        """Assumes e is an integer and removes e from self
           Raises ValueError if e is not in self"""
        try:
            self.vals.remove(e)
        except:
            raise ValueError(str(e) + ‘ not found‘)

    def intersect(self, other):
        """Assumes other is an intSet
           Returns a new intSet containing elements that appear in both sets."""
        # Initialize a new intSet    
        commonValueSet = intSet()
        # Go through the values in this set
        for val in self.vals:
            # Check if each value is a member of the other set    
            if other.member(val):
                commonValueSet.insert(val)
        return commonValueSet

    def __str__(self):
        """Returns a string representation of self"""
        self.vals.sort()
        return ‘{‘ + ‘,‘.join([str(e) for e in self.vals]) + ‘}‘

    def __len__(self):
        """Returns the length of the set.
           This method is called by the `len` built-in function."""
        return len(self.vals)