392. Is Subsequence

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

Solution:

不要想的太复杂

class Solution {
    public boolean isSubsequence(String s, String t) {
        if (s == null || s.length() == 0){
            return true;
        }

        int i = 0;
        int j = 0;

        while(i < s.length() && j < t.length()){
            if (s.charAt(i) == t.charAt(j)){
                i++;
                j++;
            }else{
                j++;
            }
        }

        if (i == s.length()){
            return true;
        }else{
            return false;
        }

    }
}

// TC: O(n)
// SC: O(1)

class Solution {
    public boolean isSubsequence(String s, String t) {
        // base case 
        if (s == null && t == null){
            return true;
        }

        if (s == null || t == null){
            return false;
        }

        if (s.length() > t.length()){
            return false;
        }

        int tpointer = 0;
        int spointer = 0;

        while (tpointer < t.length()){
            if (spointer == s.length()){
                return true;
            }
            if (t.charAt(tpointer) == s.charAt(spointer)){
                tpointer++;
                spointer++;
            }else{
                tpointer++;
            }
        }

        if (spointer == s.length()){
            return true;
        }else{
            return false;
        }
    }
}

// TC: O(n)
// SC: O(1)
/*


while( t< length)

       a h b g d c
                   t

       a b c
             s


s == s.length() 
true

*/