#Leetcode# 392. Is Subsequence

https://leetcode.com/problems/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?

class Solution {
public:
    bool isSubsequence(string s, string t) {
        int ls = s.length(), lt = t.length();
        if(!ls) return true;
        if(!lt && ls) return false;
        
        int pos = 0, temp = 0;
        while(pos <= ls && temp <= lt) {
            if(s[pos] == t[temp]) 
                pos ++;
            temp ++;
        }
        return pos == ls + 1;
    }
};