Is Subsequence

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

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).

Solution

We traverse both strings from one side to other side. If a matching character is found, we move ahead in both strings. Otherwise we move ahead only in second string.

fun isSubsequence(s: String, t: String): Boolean {
    if (s.isEmpty())
        return true
    if (t.isEmpty())
        return false
    var i = 0
    for (element in t) {
        if (s[i] == element) {
            i++
            if (i == s.length)
                return true
        }
    }
    return false
}