392.md

LeetCode 392 Is Subsequence

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?

思路：一个一个往后比较，有相等的则往后比较，比较完之后，如果s的指针到了最后则true。

code

class Solution {
    public boolean isSubsequence(String s, String t) {
        int index = -1;
        
        for(char c : s.toCharArray()) {
            index = t.indexOf(c, index + 1);

            if(index == -1) {
                return false;
            }
        }
        return true;
    }
}