hackerrank-tasks/reverse_linked_list.py at master · Saketkr21/hackerrank-tasks · GitHub

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class ListNode:
    def __init__(self, v, n):
        self.val = v
        self.next = n

def reverse(head):

    curr = head
    prev = None
    nxxt = None

    while curr != None:
#         nxxt = curr.next
#         curr.next = prev
#         prev = curr
#         curr = nxxt

        prev = curr
        next = curr.next
        curr = next

    head = prev

def print_list(head):
    l = head
    while l != None:
        print l.val,
        l = l.next
    print


def main():
    q = dict()
    for i in [4,3,2,1,0]:
        if(i+1 not in q):
            q[i+1] = None
        q[i] = ListNode(i+1,q[i+1])

    print_list(q[0])
    reverse(q[0])
    print_list(q[4])


main()

"""
1 - 2 - 3 - 4 - 5

1-3-4-5
2-1-3-4-5


2 - 1 - 3 - 4 - 5
3 - 2 - 1 - 4 - 5
...
5 - 4 - 3 - 2 - 1
"""