isSubsequence.js

/**
Given two strings s and t, return true if s is a subsequence of t, or false otherwise.

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

* @param {string} s
* @param {string} t
* @return {boolean}
*/

var isSubsequence = function (s, t) {
  if (!s && !t) return true;
  let sIndex = 0;

  for (let tIndex = 0; tIndex < t.length; tIndex++) {
    if (s[sIndex] === t[tIndex]) {
      sIndex++;
    }
    if (sIndex === s.length) {
      return true;
    }
  }
  return false;
};