题目要求：

Given a string s and a string t, check if s is subsequence of t.

You may assume that there is only lower case English letters in both s and t. t is potentially a very long (length ~= 500,000) string, and s is a short string (<=100).

A subsequence of a string is a new string which is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (ie, "ace" is a subsequence of "abcde" while "aec" is not).

Examples:
s = "abc", t = "ahbgdc"

Return true.

Example 2:
s = "axc", t = "ahbgdc"

Return false.

解题思路：

• 看了代码就很容易明白了

class Solution(object):
    def isSubsequence(self, s, t):
        """
        :param s:
        :param t:
        :return:
        """
        if not s:
            return True

        num = 0
        for i in range(len(t)):
            if s[num] == t[i]:
                num += 1
            if num == len(s):
                break

        return num == len(s)

if __name__ == "__main__":
    print(Solution.isSubsequence(self=None, s = "axc", t = "ahbxc"))