2. Is Subsequence

Given two strings s and t, check if s is a subsequence of t.

A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., "ace" is a subsequence of "abcde" while "aec" is not).

Example 1:

Input: s = "abc", t = "ahbgdc"
Output: true

Example 2:

Input: s = "axc", t = "ahbgdc"
Output: false

Solution: (Greedy)

class Solution
{
public:
    bool isSubsequence(string s, string t)
    {

        int n = t.length();
        int m = s.length();

        int i = 0, j = 0;

        while (i < n)
        {

            if (s[j] == t[i])
            {
                j++;
                i++;
            }
            else
            {
                i++;
            }
        }

        if (j == m)
        {
            return true;
        }

        return false;
    }
};

Time Complexity: O(n + m)