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:

1 2 3 4

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

Example 2:

1 2 3 4

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

/** * // 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; * }; */ classNestedIterator { private: std::vector<int> integerVector; int index; public: explicitNestedIterator(conststd::vector<NestedInteger>& nestedList){ index = 1; integerVector = std::vector<int>(1); std::function<void(conststd::vector<NestedInteger>& nestedLis)> dfs = [&](conststd::vector<NestedInteger>& roots) { for(constauto& root : roots) { if(root.isInteger()) { integerVector.push_back(root.getInteger()); } else { dfs(root.getList()); } } }; dfs(nestedList); }

intnext(){ return integerVector[index++]; }

boolhasNext(){ return index <= integerVector.size() - 1; } };

/** * Your NestedIterator object will be instantiated and called as such: * NestedIterator i(nestedList); * while (i.hasNext()) cout << i.next(); */