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 sis 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.

设置两个循环，线性遍历，从s的第一个字符开始在t中遍历，如果在t中找到对应的字符，则改变标记变量进下一个字符的遍历，如果直到t遍历完都没找到，那么说明没有subsequence，返回false。如果全部遍历找到，那么返回true。

class Solution {
public:
    bool isSubsequence(string s, string t) 
    {
        int i,j,tail = 0;
        for(i = 0;i < s.size(); i++)
        {
            for(j = tail; j < t.size(); j++)
            {
                if(s[i] == t[j])
                {
                    tail = j+1;
                    break;
                }
            }
            if(j == t.size())
            return false;
        }

            return true;

        
    }
};