- edit distance: DP
- generate paranthes: Iterative Recursive
- integer to english words: Unit(every 3) Recurvise
- interleaving string: Iterative Recusive/DP
- longest valid parenthes: Stack存分界符 (注意’)’pop分情况)
- minimum window substring: 双指针法。1，找到满足子串；2，移动start使之成为最短
- palindrom pairs: 分3种情况回文, O(n)空间换时间从O($n^2$)为O(n)
- shortest palindrom: 找到最长回文子串即可
- regular expression matching: DP
- wilcard matching: DP
- valid number: regexp/NFS
- scramble string: Substring Recursive
- word ladder II: 构建非重复前向路径
