packagemedium;

importjava.util.Iterator;

importjava.util.LinkedList;

importjava.util.List;

importjava.util.Queue;

publicclassFlatten2DVector {

}

classVector2DimplementsIterator<Integer> {

privateQueue<Integer>cache;

privateList<List<Integer>>vec2d;

publicVector2D(List<List<Integer>>vec2d) {

this.vec2d =vec2d;

this.cache =newLinkedList<Integer>();

if(vec2d !=null &&vec2d.size() >0){

for(List<Integer>list :vec2d){

for(inti :list){

cache.offer(i);

}

}

}

}

publicIntegernext() {

returncache.poll();

}

publicbooleanhasNext() {

return !cache.isEmpty();

}

}

|259|[3Sum Smaller](https://leetcode.com/problems/3sum-smaller/)|[Solution](../../blob/master/MEDIUM/src/medium/_3Sum_Smaller.java)| O(n^2)|O(1)| Medium|

|257|[Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/)|[Solution](../../blob/master/EASY/src/easy/BinaryTreePaths.java) | O(n*h) | O(h) | DFS/Recursion

|252|[Meeting Rooms](https://leetcode.com/problems/meeting-rooms/)|[Solution](../../blob/master/EASY/src/easy/MeetingRooms.java)| O(nlogn)| O(1)|

|251|[Flatten 2D Vector](https://leetcode.com/problems/flatten-2d-vector/)|[Solution](../../blob/master/MEDIUM/src/medium/Flatten2DVector.java)| O(1)|O(m*n)| Medium|

|250|[Count Univalue Subtrees](https://leetcode.com/problems/count-univalue-subtrees/)|[Solution](../../blob/master/MEDIUM/src/medium/CountUnivalueSubtrees.java)| O(n)|O(h) | Medium| DFS

|249|[Group Shifted Strings](https://leetcode.com/problems/group-shifted-strings/)|[Solution](../../blob/master/EASY/src/easy/GroupShiftedStrings.java)| O(nlogn)| O(n)|

|246|[Strobogrammatic Number](https://leetcode.com/problems/strobogrammatic-number/)|[Solution](../../blob/master/EASY/src/easy/StrobogrammaticNumber.java)| O(n)| O(1)|