(lintcode)第22题 平面列表

要求：

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。

 注意事项

如果给定的列表中的要素本身也是一个列表，那么它也可以包含列表。

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]。

思路：比较简单，直接递归调用即可。

/** * // 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> list=new ArrayList<>();        doFlatten(nestedList,list);        return list;    }     public void doFlatten(List<NestedInteger> nestedList,List<Integer> list){         if(nestedList != null){             for(int i=0;i<nestedList.size();i++){                 if(nestedList.get(i).isInteger()){                     list.add(nestedList.get(i).getInteger());                 }else{                     doFlatten(nestedList.get(i).getList(),list);                 }             }         }     }}