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思路一：最简单的思路，采用递归直接预处理出一个数组来存储结果，那么这两个函数就很好写了。但是我感觉这样的设计并不能算是迭代器。

/** * // This is the interface that allows for creating nested lists. * // You should not implement it, or speculate about its implementation * class NestedInteger { *   public: *     // Return true if this NestedInteger holds a single integer, rather than a nested list. *     bool isInteger() const; * *     // Return the single integer that this NestedInteger holds, if it holds a single integer *     // The result is undefined if this NestedInteger holds a nested list *     int getInteger() const; * *     // Return the nested list that this NestedInteger holds, if it holds a nested list *     // The result is undefined if this NestedInteger holds a single integer *     const vector
   
     &getList() const; * }; */class NestedIterator {
   public:    NestedIterator(vector
    
      &nestedList) {
           dfs(nestedList);        pos=0;        siz=vec.size();    }        int next() {
           return vec[pos++];    }        bool hasNext() {
           return pos
     

思路二：利用栈。我们搞一个$stack$存储$NestedInteger$，并且保证要么栈为空，要么栈顶的元素一定是一个数。现在考虑怎么在栈中存放数据，当我们面对一个$vector<NestedInteger>$时，递归的做法是从第一个元素依次往后处理，如果某个元素不是数字，则需要再次递归下去；用栈怎么搞呢呢？我们可以从最后一个元素开始，把他们依次放到栈中，那么栈顶元素就是第一个元素，如果此时栈顶元素不是数字，那么就需要把它弹出，得到它的$List$并继续这个过程。

/** * // This is the interface that allows for creating nested lists. * // You should not implement it, or speculate about its implementation * class NestedInteger { *   public: *     // Return true if this NestedInteger holds a single integer, rather than a nested list. *     bool isInteger() const; * *     // Return the single integer that this NestedInteger holds, if it holds a single integer *     // The result is undefined if this NestedInteger holds a nested list *     int getInteger() const; * *     // Return the nested list that this NestedInteger holds, if it holds a nested list *     // The result is undefined if this NestedInteger holds a single integer *     const vector
   
     &getList() const; * }; */class NestedIterator {
   public:    NestedIterator(vector
    
      &nestedList) {
           initstack(nestedList);    }        int next() {
           int val=s.top().getInteger();        s.pop();        return val;    }        bool hasNext() {
           //栈非空 且栈顶元素不是数字        while(!s.empty()&&!s.top().isInteger()){
               NestedInteger tmp=s.top();            s.pop();            initstack(tmp.getList());        }        return !s.empty();    }private:    stack
     
       s;    void initstack(vector
      
        &nestedList){
           int siz=nestedList.size();        //倒着放进去        for(int i=siz-1;i>=0;i--)            s.push(nestedList[i]);    }};/** * Your NestedIterator object will be instantiated and called as such: * NestedIterator i(nestedList); * while (i.hasNext()) cout << i.next(); */
      
     
    
   

思路三：利用python的生成器。

# """# This is the interface that allows for creating nested lists.# You should not implement it, or speculate about its implementation# """#class NestedInteger:#    def isInteger(self) -> bool:#        """#        @return True if this NestedInteger holds a single integer, rather than a nested list.#        """##    def getInteger(self) -> int:#        """#        @return the single integer that this NestedInteger holds, if it holds a single integer#        Return None if this NestedInteger holds a nested list#        """##    def getList(self) -> [NestedInteger]:#        """#        @return the nested list that this NestedInteger holds, if it holds a nested list#        Return None if this NestedInteger holds a single integer#        """class NestedIterator:    def __init__(self, nestedList: [NestedInteger]):                def gen(nestedList):            for each in nestedList:                if each.isInteger():                    yield each.getInteger()                else:                    yield from gen(each.getList())                self.iterator=gen(nestedList)        try:            self.value=next(self.iterator)        except StopIteration:            self.value=None    def next(self) -> int:        ans=self.value        try:            self.value=next(self.iterator)        except StopIteration:            self.value=None        return ans        def hasNext(self) -> bool:        return self.value!=None         # Your NestedIterator object will be instantiated and called as such:# i, v = NestedIterator(nestedList), []# while i.hasNext(): v.append(i.next())

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