|139|[Word Break](https://leetcode.com/problems/word-break/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_139.java)| O(n^2)|O(n) | Medium| DP

|138|[Copy List with Random Pointer](https://leetcode.com/problems/copy-list-with-random-pointer/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_138.java)| O(n)|O(n) | Medium| LinkedList, HashMap

|137|[Single Number II](https://leetcode.com/problems/single-number-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_137.java)| O(n)|O(n) | Medium|

|135|[Candy](https://leetcode.com/problems/candy/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_135.java)| O(n)|O(1) | Hard| Greedy

|134|[Gas Station](https://leetcode.com/problems/gas-station/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_134.java)| O(n)|O(1) | Medium| Greedy

|133|[Clone Graph](https://leetcode.com/problems/clone-graph/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_133.java)| O(n)|O(n) | Medium| HashMap, BFS, Graph

//approach 1: use set, since this problem explicitly states that every element appears twice and only one appears once

//so, we could safely remove the ones that are already in the set, O(n) time and O(n) space.

//HashTable approach works similarly like this one, but it could be more easily extend to follow-up questions.