Time:O(n) Space:O(1) C++ class Solution { public: bool isSubsequence(string s, string t) { if (s.empty()) return true; int i = 0; for (const char c : t) if (s[i] == c && ++i == s.length()) return true; return false; } }; JAVA class Solution { public boolean isSubsequence(String s, String t) { if (s.isEmpty()) return true; int i = 0; for (final char c : t.toCharArray()) if (s.charAt(i) == c && ++i == s.length()) return true; return false; } }