Flatten Nested List Iterator in Python

PythonServer Side ProgrammingProgramming

Suppose we have a nested list of integers; we have to implement an iterator to flatten it. Each element is either an integer, or a list. The elements of that list may also be integers or other lists. So if the input is like [[1, 1], 2, [1, 1]], then the output will be [1, 1, 2, 1, 1]

To solve this, we will follow these steps −

  • In the initializing section, it will take the nested list, this will work as follows −

  • set res as empty list, index := 0, call getVal(nestedList)

  • The getVal() will take nestedIntegers, this will work as −

  • for i in nestedIntegers

    • if i is an integer, then then insert the i into res array, otherwise call getVal(the i list)

  • The next() method will return the value pointed by index, and increase index by 1

  • the hasNext() will return true, when there is an element next to it, otherwise false

Example

Let us see the following implementation to get better understanding −

class NestedIterator(object):
   def __init__(self, nestedList):
      """
      Initialize your data structure here.
      :type nestedList: List[NestedInteger]
      """
      self.res = []
      self.index = 0
      self.getVal(nestedList)
      #print(self.res)
   def getVal(self,NestedInteger):
      for i in NestedInteger:
         if(i.isInteger()):
            self.res.append(i.getInteger())
         else:
            self.getVal(i.getList())
   def next(self):
      """
      :rtype: int
      """
      self.index+=1
      return self.res[self.index-1]
   def hasNext(self):
      """
      :rtype: bool
      """
      if self.index == len(self.res):
         return False
      return True

Input

[[1,1],2,[1,1]]

Output

[1,1,2,1,1]
raja
Published on 17-Mar-2020 06:07:00
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