[Vssue]0647.回文子串.md

[youngyangyang04]

https://www.programmercarl.com/0647.%E5%9B%9E%E6%96%87%E5%AD%90%E4%B8%B2.html

[Du1in9]

如果字符 s[i] 与字符 s[j] 相同，那么：
若 j - i = 0，例如 1 - 1 = 0，则 a 是回文子串
若 j - i = 1，例如 2 - 1 = 1，则 aa 是回文子串
若 j - i > 1，且 i+1 到 j-1 也是回文子串。例如 b 是回文子串，则 aba 也是。

// 例: s = "aaa"
i = 2:
  j = 2: 满足 'a' == 'a', 满足 2-2 <= 1 (情况一), result = 1, dp[2][2] = t
i = 1:
  j = 1: 满足 'a' == 'a', 满足 1-1 <= 1 (情况一), result = 2, dp[1][1] = t
  j = 2: 满足 'a' == 'a', 满足 2-1 <= 1 (情况二), result = 3, dp[1][2] = t
i = 0:
  j = 0: 满足 'a' == 'a', 满足 0-0 <= 1 (情况一), result = 4, dp[0][0] = t
  j = 1: 满足 'a' == 'a', 满足 1-0 <= 1 (情况二), result = 5, dp[0][1] = t
  j = 2: 满足 'a' == 'a', 满足 dp[1][1] = t (情况三), result = 6, dp[0][2] = t