LeetCode 392. Is Subsequence

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). Example 1: s = “abc”, t = “ahbgdc” Return true. Example 2: s = “axc”, t = “ahbgdc” Return false. Follow up: If there are lots of incoming S, say S1, S2, … , Sk where k >= 1B, and you want to check one by one to see if T has its subsequence. In this scenario, how would you change your code?

题目大意:判断s是否是t的子串~

分析:设立两个指针p和q,分别指向s[0]和t[0],只要p和q没有超出s和t的长度范围,不断判断当前s[p]与t[q]是否相等,如果不相等就将q指针不断后移,直到相等为止~相等后p和q指针同时后移,依次判断~
最终判断p指针是否等于lens,即p指针是否指完了s字符串的所有字符~