Merge pull request #41 from miguelHx/miguel_2.5_sum_lists

Miguel 2.5 - Sum Lists [Python]

Author: lhchavez

Python/chapter02/2.5 - Sum Lists/miguel_2.5_soln.py

@@ -0,0 +1,396 @@
+"""
+Python version 3.7.0
+2.5 - Sum Lists
+You have two numbers represented by a linked list,
+where each node contains a single digit.
+The digits are stored in reverse order, such that
+the 1's digit is at the head of the list.  Write a
+function that adds the two numbers and returns the sum
+as a linked list.
+EXAMPLE
+Input:  (7 -> 1 -> 6) + (5 -> 9 -> 2). That is, 617 + 295
+Result: 2 -> 1 -> 9. That is, 912
+FOLLOW UP
+Suppose the digits are stored in forward order.
+Repeat the above problem.
+EXAMPLE
+Input:  (6 -> 1 -> 7) + (2 -> 9 -> 5). That is, 617 + 295
+Result: 9 -> 1 -> 2. That is, 912
+"""
+import unittest
+
+
+class Node:
+    def __init__(self, d: int):
+        self.data = d
+        self.next = None
+
+    def __repr__(self):
+        return self.__str__()
+
+    def __str__(self):
+        return '<Node Value: {}>'.format(self.data)
+
+    def __eq__(self, other: object):
+        if not isinstance(other, Node):
+            return NotImplemented
+        return self.data == other.data
+
+
+class LinkedList:
+    def __init__(self, *numbers: int):
+        self.head = None
+        self.tail = None
+        self.size = 0
+        for num in numbers:
+            self.append_to_tail(num)
+
+    def append_to_tail(self, e) -> None:
+        if isinstance(e, int):
+            self._append_num(e)
+        elif isinstance(e, Node):
+            self._append_node(e)
+
+    def _append_num(self, d: int) -> None:
+        if self.head is None:
+            self.head = Node(d)
+            self.tail = self.head
+        else:
+            end = Node(d)
+            self.tail.next = end
+            self.tail = end
+        self.size += 1
+
+    def _append_node(self, n: Node) -> None:
+        if self.head is None:
+            self.head = n
+            self.tail = self.head
+        else:
+            end = n
+            self.tail.next = end
+            self.tail = end
+        self.size += 1
+
+    def append_to_head(self, d: int) -> None:
+        new_head = Node(d)
+        new_head.next = self.head
+        if self.head is None:
+            # if list is empty and we add
+            # out first element, head AND tail
+            # must point to same node
+            self.tail = new_head
+        self.head = new_head
+        self.size += 1
+
+    def get_node_at(self, index: int) -> Node:
+        if index < 0 or index >= self.size:
+            raise IndexError('list index out of range')
+        n = self.head
+        for i in range(self.size):
+            if i == index:
+                return n
+            n = n.next
+
+    def pop_head(self) -> Node:
+        if self.head is None:
+            raise IndexError('no head to pop')
+        h = self.head
+        h.next = None
+        self.head = self.head.next
+        self.size -= 1
+        return h
+
+    def append(self, ll: 'LinkedList') -> None:
+        self.tail.next = ll.head
+        self.size += ll.size
+        ll.head = None
+        ll.size = 0
+
+    def reverse(self) -> None:
+        """
+        Reverses this linked list in place
+        :return:
+        """
+        if self.head is None:
+            return
+        prev = self.head
+        self.tail = prev
+        curr = prev.next
+        self.tail.next = None
+        while curr is not None:
+            old_next = curr.next
+            curr.next = prev
+            prev = curr
+            curr = old_next
+        self.head = prev
+
+    def __repr__(self):
+        return self.__str__()
+
+    def __str__(self):
+        if self.head is None:
+            return '<empty>'
+        ll = []
+        n = self.head
+        while n.next is not None:
+            ll.append('{} -> '.format(n.data))
+            n = n.next
+        ll.append(str(n.data))
+        return ''.join(ll)
+
+    def __eq__(self, other: object):
+        if not isinstance(other, LinkedList):
+            return NotImplemented
+        a = self.head
+        b = other.head
+        while a is not None and b is not None:
+            if a.data != b.data:
+                return False
+            # otherwise, advance both pointers
+            a = a.next
+            b = b.next
+        return a is None and b is None
+
+
+def reverse_linked_list(ll: LinkedList) -> LinkedList:
+    """
+    Takes in a linked list and returns a reversed copy
+    :param ll: input linked list
+    :return: reversed linked list
+    """
+    output_ll = LinkedList()
+    n = ll.head
+    while n is not None:
+        output_ll.append_to_head(n.data)
+        n = n.next
+    return output_ll
+
+
+def sum_lists_forward(ll1: LinkedList, ll2: LinkedList) -> LinkedList:
+    """
+    Will add ll1 and ll2 where each element in the linked lists
+    represent digits.
+    Note: Each element in the input linked lists MUST be values
+    between 0-9
+    Digits are in forward order, for example:
+    Input: (6 -> 1 -> 7) + (2 -> 9 -> 5). That is, 617 + 295
+    Output: 9 -> 1 -> 2. That is, 912
+    Runtime: O(n)
+    Space Complexity: O(n) - output_ll
+    :param ll1: first input linked list
+    :param ll2: second input linked list
+    :return: a linked list containing the result of the addition
+    """
+    # reverse both lists
+    reversed_ll1 = reverse_linked_list(ll1)
+    reversed_ll2 = reverse_linked_list(ll2)
+    # then, call sum_lists
+    reversed_result = sum_lists(reversed_ll1, reversed_ll2)
+    # reverse a final time
+    reversed_result.reverse()
+    return reversed_result
+
+
+def sum_lists(ll1: LinkedList, ll2: LinkedList) -> LinkedList:
+    """
+    Will add ll1 and ll2 where each element in the linked lists
+    represent digits.
+    Note: Each element in the input linked lists MUST be values
+    between 0-9
+    Digits are in backward order, for example:
+    Input:  (7 -> 1 -> 6) + (5 -> 9 -> 2). That is, 617 + 295
+    Result: 2 -> 1 -> 9. That is, 912
+    Runtime: O(n)
+    Space Complexity: O(n) - output_ll
+    :param ll1: first input linked list
+    :param ll2: second input linked list
+    :return: a linked list containing the result of the addition
+    """
+    shorter_ll, longer_ll = (ll1, ll2) if ll1.size < ll2.size else (ll2, ll1)
+    n1 = shorter_ll.head
+    n2 = longer_ll.head
+    output_ll = LinkedList()
+    carry = 0
+    while n1 is not None:
+        first = n1.data
+        second = n2.data
+        result = first + second + carry
+        if result >= 10:
+            carry = 1
+            result -= 10  # extract digit in one's place
+        else:
+            carry = 0
+        output_ll.append_to_tail(result)
+        n1 = n1.next
+        n2 = n2.next
+    # loop through remaining longer list
+    while n2 is not None:
+        value = n2.data
+        result = value + carry
+        if result >= 10:
+            carry = 1
+            result -= 10
+        else:
+            carry = 0
+        output_ll.append_to_tail(result)
+        n2 = n2.next
+    if carry > 0:
+        output_ll.append_to_tail(carry)
+    return output_ll
+
+
+class TestSumLists(unittest.TestCase):
+
+    def setUp(self):
+        self.test_cases = [
+            (
+                LinkedList(7, 1, 6),
+                LinkedList(5, 9, 2),
+                LinkedList(2, 1, 9)
+            ),
+            (
+                LinkedList(1, 1, 1, 1),
+                LinkedList(2, 2, 2, 2),
+                LinkedList(3, 3, 3, 3)
+            ),
+            (
+                LinkedList(5),
+                LinkedList(4),
+                LinkedList(9)
+            ),
+            (
+                LinkedList(5),
+                LinkedList(6),
+                LinkedList(1, 1)
+            ),
+            (
+                LinkedList(7, 1, 9),
+                LinkedList(5, 9, 2),
+                LinkedList(2, 1, 2, 1)
+            ),
+            (
+                LinkedList(9, 9, 9, 9),
+                LinkedList(9, 9, 9, 9),
+                LinkedList(8, 9, 9, 9, 1)
+            ),
+            (
+                LinkedList(9, 9, 9, 9),
+                LinkedList(9, 9),
+                LinkedList(8, 9, 0, 0, 1)
+            ),
+            (
+                LinkedList(1, 2),
+                LinkedList(1),
+                LinkedList(2, 2)
+            ),
+            (
+                LinkedList(5),
+                LinkedList(2, 1),
+                LinkedList(7, 1)
+            ),
+            (
+                LinkedList(),
+                LinkedList(1),
+                LinkedList(1)
+            ),
+            (
+                LinkedList(),
+                LinkedList(),
+                LinkedList()
+            )
+        ]
+
+        self.forward_test_cases = [
+            (
+                LinkedList(6, 1, 7),
+                LinkedList(2, 9, 5),
+                LinkedList(9, 1, 2)
+            ),
+            (
+                LinkedList(1, 1, 1, 1),
+                LinkedList(2, 2, 2, 2),
+                LinkedList(3, 3, 3, 3)
+            ),
+            (
+                LinkedList(3),
+                LinkedList(2),
+                LinkedList(5)
+            ),
+            (
+                LinkedList(5),
+                LinkedList(6),
+                LinkedList(1, 1)
+            ),
+            (
+                LinkedList(9, 9, 9, 9),
+                LinkedList(9, 9, 9, 9),
+                LinkedList(1, 9, 9, 9, 8)
+            ),
+            (
+                LinkedList(9, 9, 9, 9),
+                LinkedList(9, 9),
+                LinkedList(1, 0, 0, 9, 8)
+            ),
+            (
+                LinkedList(1, 2),
+                LinkedList(4),
+                LinkedList(1, 6)
+            ),
+            (
+                LinkedList(4, 2),
+                LinkedList(5),
+                LinkedList(4, 7)
+            ),
+            (
+                LinkedList(4, 2),
+                LinkedList(9),
+                LinkedList(5, 1)
+            ),
+            (
+                LinkedList(8, 2),
+                LinkedList(4),
+                LinkedList(8, 6)
+            ),
+            (
+                LinkedList(9, 1, 0, 2),
+                LinkedList(1, 0),
+                LinkedList(9, 1, 1, 2)
+            ),
+            (
+                LinkedList(9, 1, 9, 2),
+                LinkedList(1, 0),
+                LinkedList(9, 2, 0, 2)
+            ),
+            (
+                LinkedList(9, 9, 1, 9),
+                LinkedList(2, 0),
+                LinkedList(9, 9, 3, 9)
+            ),
+            (
+                LinkedList(),
+                LinkedList(1),
+                LinkedList(1)
+            ),
+            (
+                LinkedList(),
+                LinkedList(),
+                LinkedList()
+            ),
+            (
+                LinkedList(1, 2, 3),
+                LinkedList(),
+                LinkedList(1, 2, 3)
+            )
+        ]
+
+    def test_sum_lists_forward_order(self):
+        for ll1, ll2, expected in self.forward_test_cases:
+            self.assertEqual(sum_lists_forward(ll1, ll2), expected, msg=(ll1, ll2))
+
+    def test_sum_lists(self):
+        for ll1, ll2, expected in self.test_cases:
+            self.assertEqual(sum_lists(ll1, ll2), expected, msg=(ll1, ll2))
+
+
+if __name__ == '__main__':
+    unittest.main()