392. Is Subsequence

Posted 2020-12-15 wentiliangkaihua

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

You may assume that there is only lower case English letters in both s and t. t is potentially a very long (length ~= 500,000) string, and s is a short string (<=100).

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:
s = "abc", t = "ahbgdc"

Return true.

Example 2:
s = "axc", t = "ahbgdc"

Return false.

Follow up:
If there are lots of incoming S, say S1, S2, ... , Sk where k >= 1B, and you want to check one by one to see if T has its subsequence. In this scenario, how would you change your code?

Credits:
Special thanks to @pbrother for adding this problem and creating all test cases.

class Solution {
    public boolean isSubsequence(String s, String t) {
        if (t.length() == 0 && s.length() == 0) return true;
        if(s.length() == 0) return true;
        if(t.length() == 0) return false;
        int ind = 0;
        
        for(int i = 0; i < t.length(); i++){
            if(s.charAt(ind) == t.charAt(i)){
                if(ind == s.length() - 1) return true;
                ind++;
            }
        }
        return false;
    }
}

非dp方法，匹配完就是true，匹配不完就是false

然后试了两个dp还memory limit了草