Leetcode 392. Is Subsequence (Medium) (cpp)

Leetcode 392. Is Subsequence (Medium) (cpp)
Tag: Binary Search, Dynamic Programming, Greedy
Difficulty: Medium

/*

392. Is Subsequence (Medium)

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?

*/
class Solution {
public:
    bool isSubsequence(string s, string t) {
        int s_i = 0;
        for (int t_i = 0; t_i < t.length() && s_i < s.length(); t_i++)
            if (t[t_i] == s[s_i]) s_i++;
        return s_i == s.length();
    }
};