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Derek Derek
8,744 Points[python] recursion stops in the middle
I would like to find ALL pairs that sum to x in a linked list, but the code I have right now only finds the first such pair. How can i modify my recursive function to find the second pair in my example (i.e., catch 5, 7 pair) as well?
class Node:
def __init__(self, val):
self.val = val
self.next = None
self.prev = None
class LinkedList:
'''doubly linked list'''
def __init__(self, head):
self.head = Node(head)
self.tail = None
self.pairs = []
self.length = 1
def add(self, item):
cur = self.head
while cur.next is not None:
cur = cur.next
cur.next = Node(item)
self.length += 1
# make linked list doubly
cur.next.prev = cur
# set tail of linked list
self.tail = cur.next
def findSummingPair(self, x, head, tail):
current_sum = head.val + tail.val
if current_sum == x:
self.pairs.append((head.val, tail.val))
else:
if current_sum < x:
# print current_sum, x
return self.findSummingPair(x, head.next, tail)
else:
# print current_sum, x
return self.findSummingPair(x, head, tail.prev)
return self.pairs
ll = LinkedList(1)
ll.add(2)
ll.add(5)
ll.add(7)
ll.add(10)
ll.add(15)
# print ll.head.next.next.prev.val
# print ll.tail.val
print ll.findSummingPair(12, ll.head, ll.tail)