双指针判断

#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param S string字符串 
# @param T string字符串 
# @return bool布尔型
#
class Solution:
    def isSubsequence(self , S: str, T: str) -> bool:
        # write code here
        si = ti = 0
        while ti < len(T):
            if T[ti] == S[si]:
                si += 1
                if si == len(S):
                    return True
            ti += 1
        return False