pay attention to subsequence and substring

longest-palindromic-subsequence Solution 这个是subset 区别这个和subsequence dp 数组的定义是 dp[i][j]=x的定义是，string[i:j]内的最长回文子序列的长度。二维dp 所以这个题目迭代的时候要从最后开始迭代，j却要从 range(i+1，n)内迭代。 if the length of string is 7, the last index of the string is 6 Then the sequence of (i,j) will be 5,6 4,5 4,6 3,4 -word-break Solution 一维dp数组，返回值是true or false

-word-break-ii Solution 这个用的是回溯 def backtrack(start,track), 选择列表是 word list

-palindrome-number Solution 这是左右指针的问题不过这个可以用来当判断一个序列是否是回文串 palindrome 。It ask you if a number is a palindrome number

palindromic-substrings Solution Given a string s, return the number of palindromic substrings in it. 同样是利用这个dp数组

for i in range(n-1,-1,-1):
    for j in range(i+1,n):
        dp[i][j]=(s[i]==s[j]) and dp[i+1][j-1]

Input: s = "aaa"
Output: 6
Explanation: Six palindromic strings: "a", "a", "a", "aa", "aa", "aaa".

longest-palindrome Solution ultilized counter from collections ,最后是用数学的方式在处理的这个问题
palindrome-partitioning Solution

Output: [["a","a","b"],["aa","b"]]

utilize the dp[i][j] palindrome first then backtracking, for j in range(start,n), determine if dp[start][j] is a palindrome

longest-palindromic-substring Solution 同样利用

for i in  range(n-1,-1,-1):
  for j in range(i+1,n):
    dp[i][j] = (s[i] == s[j]) and dp[i + 1][j - 1]

valid-anagram
group-anagrams Solution 这个是哈希表的使用