leetcode_c++：栈：Flatten Nested List Iterator（341）

Given a nested list of integers, implement an iterator to flatten it.

Each element is either an integer, or a list – whose elements may also be integers or other lists.

Example 1:
Given the list [[1,1],2,[1,1]],

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1].

Example 2:
Given the list [1,[4,[6]]],

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,4,6].

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/** * // 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<NestedInteger> &getList() const; * }; */class NestedIterator {  public:      void DFS(vector<NestedInteger> &nestedList)      {          for(auto val: nestedList)          {              if(val.isInteger())                  vec.push_back(val.getInteger());              else DFS(val.getList());          }      }      NestedIterator(vector<NestedInteger> &nestedList):index(0), vec() {          DFS(nestedList);          }      int next() {          return vec[index++];      }      bool hasNext() {          if(index < vec.size())              return true;          return false;      }  private:      int index;      vector<int> vec;  };  /** * Your NestedIterator object will be instantiated and called as such: * NestedIterator i(nestedList); * while (i.hasNext()) cout << i.next(); */