Easy_Question18 : Is Subsequence

• 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).

Example 1:
input: s = "abc", t = "ahbgdc"
Output: true
Example 2:
Input: s = "axc", t = "ahbgdc"
Output: false

Solution :

public boolean isSubsequence(String s, String t) {
    if(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++;

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

Time Complexity

O(min(M , N)) as we keep iterating until i or j becomes zero. M and N are the lengths of the strings.

Space Complexity

O(1) as we use constant space in the memory.