Flatten Nested List Iterator - Medium - L
Published:
Question
- https://leetcode.com/problems/flatten-nested-list-iterator/
You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it.
Implement the NestedIterator class:
NestedIterator(List
Approach
- DFS
Solution
/**
* // 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 {
vector<int> vec;
int index = 0;
void dfs(vector<NestedInteger> &nestedList){
for(auto& list: nestedList){
if(list.isInteger()){
vec.push_back(list.getInteger());
}
else{
dfs(list.getList());
}
}
}
public:
NestedIterator(vector<NestedInteger> &nestedList) {
dfs(nestedList);
}
int next() {
return vec[index++];
}
bool hasNext() {
return index < vec.size();
}
};
/**
* Your NestedIterator object will be instantiated and called as such:
* NestedIterator i(nestedList);
* while (i.hasNext()) cout << i.next();
*/