問題描述：

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"

    利用貪心算數的策略，t為母序列，s為子序列，如果在t中找到了s的某個字元，就立馬檢測下一個，t也指向下一個字元。

code:

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