题目：
题解：
class Solution:def isSubsequence(self, s: str, t: str) -> bool:n, m = len(s), len(t)f = [[0] * 26 for _ in range(m)]f.append([m] * 26)for i in range(m - 1, -1, -1):for j in range(26):f[i][j] = i if ord(t[i]) == j + ord('a') else f[i + 1][j]add = 0for i in range(n):if f[add][ord(s[i]) - ord('a')] == m:return Falseadd = f[add][ord(s[i]) - ord('a')] + 1return True
