[leetcode]392. Is Subsequence 验证子序列

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).

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?

题意：

给定串串s和t, 判断s是否是t的subsequence

思路：

指针count用来scan串串s

指针i用来scan串串t

从左至右，若t当前的字符等于s当前字符，count++

若count等于s.length()，说明s中的每个字符都包含在串串t中，最终说明s是t的subsequence

代码：

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