algorithm - Flatten out a list in java -

i asked question in interview

given hypothetical list in java that, along holding integer content, may hold list of similar type

example: [1,3,5,[6,7],8,9,10,[11,13,15,[16,17,[18,19]]],20]

output should be:

[1,3,5,6,7,8,9,10,11,13,15,16,17,18,19,20] 

easy thought! came recursive solution solved problem! or not?

the interviewer said sublists go down depths , hence may result in stackoverflow error!

i tried coming non recursive solution, couldn't. tell non recursive solution might be?

you can use linkedlist stack.

public static list<object> flattennonrecursive(list<object> list) {     list<object> result = new arraylist<>();     linkedlist<object> stack = new linkedlist<>(list);     while (!stack.isempty()) {         object e = stack.pop();         if (e instanceof list<?>)             stack.addall(0, (list<?>)e);         else             result.add(e);     }     return result; }  public static list<object> list(object... args) {     return arrays.aslist(args); }  public static void main(string[] args) {     list<object> list = list(1, 3, 5, list(6, 7), 8, 9, 10, list(11, 13, 15, list(16, 17, list(18, 19))), 20);     system.out.println("flatten=" + flattennonrecursive(list)); } 

result

flatten=[1, 3, 5, 6, 7, 8, 9, 10, 11, 13, 15, 16, 17, 18, 19, 20]