平面排列（非递归实现）

给定一个列表，该列表中的每个要素要么是个列表，要么是整数。将其变成一个只包含整数的简单列表。

样例
给定 [1,2,[1,2]]，返回 [1,2,1,2]。

给定 [4,[3,[2,[1]]]]，返回 [4,3,2,1]。

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * public interface NestedInteger {
 *
 *     // @return true if this NestedInteger holds a single integer,
 *     // rather than a nested list.
 *     public boolean isInteger();
 *
 *     // @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();
 *
 *     // @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> data = new ArrayList<Integer>();
        if(nestedList == null){
            return null;
        }
        
        for(int k = 0; k < nestedList.size(); k++){
            if(nestedList.get(k).getInteger() != null){
                data.add(nestedList.get(k).getInteger());
            }else{
                Queue<NestedInteger> list = new LinkedList();
                list.offer(nestedList.get(k));
                boolean b = true;
                while(b){
                    int size = list.size();
                    b = false;
                    for(int i = 0; i < size; i++){
                        NestedInteger vo = list.poll();
                        if(vo.getInteger() != null){
                            // data.add(vo.getInteger());
                            list.offer(vo);
                        }else{
                            b = true;
                            for(int j = 0; j < vo.getList().size(); j++){
                                list.offer(vo.getList().get(j));
                            }
                        }
                    }
                }
                int size = list.size();
                for(int i = 0; i < size; i++){
                    NestedInteger vo = list.poll();
                    data.add(vo.getInteger());
                }
            }
        }
        return data;
    }
}