1 /** 2  * // This is the interface that allows for creating nested lists. 3  * // You should not implement it, or speculate about its implementation 4  * public interface NestedInteger { 5  * 6  *     // @return true if this NestedInteger holds a single integer, rather than a nested list. 7  *     public boolean isInteger(); 8  * 9  *     // @return the single integer that this NestedInteger holds, if it holds a single integer10  *     // Return null if this NestedInteger holds a nested list11  *     public Integer getInteger();12  *13  *     // @return the nested list that this NestedInteger holds, if it holds a nested list14  *     // Return null if this NestedInteger holds a single integer15  *     public List
     
       getList();16  * }17  */18 public class NestedIterator implements Iterator
      
        {19     private Deque
       
         flatten;20     public NestedIterator(List
        
          nestedList) {21         flatten = new LinkedList<>();22         getFlatten(nestedList);23     }24     25     private void getFlatten(List
         
           nestedList) {26         for (int i = 0; i < nestedList.size(); i++) {27             if (nestedList.get(i).isInteger()) {28                 flatten.offer(nestedList.get(i).getInteger());29             } else {30                 getFlatten(nestedList.get(i).getList());31             }32         }33     }34 35     @Override36     public Integer next() {37         return flatten.pollFirst();38     }39 40     @Override41     public boolean hasNext() {42         return flatten.size() > 0;43     }44 }45 46 /**47  * Your NestedIterator object will be instantiated and called as such:48  * NestedIterator i = new NestedIterator(nestedList);49  * while (i.hasNext()) v[f()] = i.next();50  */