算法第八周 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?

思路：采用双指针，一次遍历即可，只要字符串t中含有s的所有元素即可。即在结束时判断指向s的指针是否指向末尾

class Solution {public:    bool isSubsequence(string s, string t) {       if(s.size()>t.size()) return false;          int len1 = s.size(), len2 = t.size(), k1 = 0, k2 = 0;          while(k1 < len1 && k2 < len2)          {              if(s[k1]==t[k2]) k1++;              k2++;          }          return k1 == len1;     }};