# Flatten List

## Problem

Given a list, each element in the list can be a list or integer. flatten it into a simply list with integers.

If the element in the given list is a list, it can contain list too.

## Example

Given [1,2,[1,2]], return [1,2,1,2].

Given [4,[3,[2,[1]]]], return [4,3,2,1].

## Code - Java

/**
* // This is the interface that allows for creating nested lists.
* // You should not implement it, or speculate about its implementation
* public interface NestedInteger {
* <p>
* // @return true if this NestedInteger holds a single integer,
* // rather than a nested list.
* public boolean isInteger();
* <p>
* // @return the single integer that this NestedInteger holds,
* // if it holds a single integer
* // Return null if this NestedInteger holds a nested list
* public Integer getInteger();
* <p>
* // @return the nested list that this NestedInteger holds,
* // if it holds a nested list
* // Return null if this NestedInteger holds a single integer
* public List<NestedInteger> getList();
* }
*/
public class Solution {

// @param nestedList a list of NestedInteger
// @return a list of integer
public List<Integer> flatten(List<NestedInteger> nestedList) {
// Write your code here
List<Integer> result = new ArrayList<>();

for (NestedInteger i : nestedList) {
if (i.isInteger()) {
}