string字符串
890. Find and Replace Pattern
You have a list of words and a pattern, and you want to know which words in words matches the pattern.
Input: words = [“abc”,”deq”,”mee”,”aqq”,”dkd”,”ccc”], pattern = “abb”
Output: [“mee”,”aqq”]
备注: 字符和数字转换，unordered_map
array数组
math数学
204. Count Primes
Count the number of prime numbers less than a non-negative number, n.
Input: 10
Output: 4
备注: 数学题，注意边界条件，vector标记count
递归
22. Generate Parentheses
Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.
备注: helper函数, string拼接, 递归生成vector