• Bottom-Up approach:
  more intuitive. The key is to think about how to build solution for one case off of the previous case

• Top-Down approach:
  how to divide the problem for case N into subproblems, be careful of overlap between cases.

Problem description:

Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.

Problem description:

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.

Problem description:

Given an unsorted integer array, find the smallest missing positive integer.

Problem description:

Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order.

Problem description:

Given an array nums and a value val, remove all instances of that value in-place and return the new length.

Problem description:

Given a sorted array nums, remove the duplicates in-place such that each element appear only once and return the new length.

Problem description:

Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.

Initialize of customize priority queue:

1. define a struct of compare function.
2. note the init method of pq.

Problem description:

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.