[ Python - Can't code iteration or recursion ]

I have this list and a start point as below:

lst = [[0, 1], [0, 4], [3, 4], [5, 1], [5, 2]]
point = 3 

I want to write a function that gives me this list in return: [3,4,0,1,5,2]. It takes start point, finds the pair containing the start point and takes its other half as the new start point.

Given list is an example, length of the list is not specified.

I tried to write a for function but, since the length of the list is not constant, it doesn't give the correct output

What I tried:

  def func(start,lst):
      for i in range(len(lst)):
          if lst[i][1]==start:
              cont==lst[i][0]
              lst2=lst.remove(lst[i])
          if lst[i][0]==start:
              cont==lst[i][1]
              lst2=lst.remove(lst[i])
      func(cont,lst2)

Answer 1

How about this (without using recursion):

def func(lst, start):
    result = []
    while True:
        found = False
        for item in lst:
            if start in item:
                item.remove(start)
                result.append(start)
                found = True
                if item:
                    start = item[0]
                    item.remove(start)
                    break
        if not found:
            result.append(start)
            break
    return result

Usage:

>>> func([[0, 1], [0, 4], [3, 4], [5, 1], [5, 2]], 3)
[3, 4, 0, 1, 5, 2]

Answer 2

You need something like:

def func(start, lst, out=None):
    if out is None: # create new output list on first call
        out = []
    out.append(start) # add the starting value
    if len(lst) == 0: # base case
        return out
    for i in range(len(lst)):
        if start in lst[i]: # find the node
            item = lst.pop(i) # remove the node
            next_ = item[0] if item[1] == start else item[1] # get next 'start'
            return func(next_, lst, out) # recurse

I get:

>>> func(3, [[0, 1], [0, 4], [3, 4], [5, 1], [5, 2]])
[3, 4, 0, 1, 5, 2]