LeetCode 0392 - Is Subsequence

Is Subsequence

Desicription

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?

Solution

class Solution {
public:
    bool isSubsequence(const std::string& s, const std::string& t) {
        unsigned int index = 0;
        for(const auto& c : t) {
            if(index < s.size() && c == s[index]) {
                index++;
            }
        }
        return index == s.size();
    }
};