392. Is Subsequence

内容：

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 sis 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).

思路:

判断一个字符串是否是另一个字符串的子序列，如果s是t的子序列，t可以这样构成：在s字符串中的任意位置插入任意长度的字符串。

【思路】

1.维持两个字符串指针，分别指向s和t，如果当前字符相同，则指针都向后移动，否则只移动t的指针，直到s中出现的字符都在t中出现过了，我们可以判定s是t的子序列。代码如下：

public class Solution {
    public boolean isSubsequence(String s, String t) {
        int sindex = 0, tindex = 0;
        while(sindex < s.length() && tindex < t.length()) {
            if(s.charAt(sindex) == t.charAt(tindex)) {
                sindex++;
            }
            tindex++;
        }
        if(sindex == s.length()) return true;
        return false;
    }
}