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.

題意就是輸入兩個字串，判斷一個字串是否可以由另外一個字串刪除一些字母得到。容易想到的一個貪心演算法就是，只要遍歷一遍t字串，依次找出s字串的每個字元。時間複雜度為o(n)。

class Solution {
public:
    bool isSubsequence(string s, string t) {
        int index = 0;
        int
 
 s_pos = s[index];
        for (int i = 0; i < t.length(); i++) {
            if (t[i] == s_pos) {
                index++;
                s_pos = s[index];

            }

        }
        if (index == s.length()) {
            return true;
        }
        else {
            return false;
        }
    }
};