341. Flatten Nested List Iterator

/*
 * 341. Flatten Nested List Iterator
 * 2016-7-10 by Mingyang
 * 这个题目又是Iterator，这里不能直接用那个东西了
 * 而且我们知道List可以从最后一个往前遍历
 */
 class NestedIterator implements Iterator<Integer> {
    Stack<NestedInteger> stack = new Stack<>();
    public NestedIterator(List<NestedInteger> nestedList) {
        for(int i = nestedList.size() - 1; i >= 0; i--) {
            stack.push(nestedList.get(i));
        }
    }
    @Override
    public Integer next() {
        return stack.pop().getInteger();
    }

    @Override
    public boolean hasNext() {
        while(!stack.isEmpty()) {
            NestedInteger curr = stack.peek();
            if(curr.isInteger()) {
                return true;
            }
            stack.pop();
            for(int i = curr.getList().size() - 1; i >= 0; i--) {
                stack.push(curr.getList().get(i));
            }
        }
        return false;
    }
    @Override
    public void remove() {
        // TODO Auto-generated method stub
        
    }
}
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();
}