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?

解题要点：

遍历s的每个字符，在t里面查找是否有该字符，如没有，立即返回false。

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;
    }
}