Is Subsequence 392

Question

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?

Solution

这道题解法很直接，遍历s中的每个字符，和t中的字符进行匹配，如果s先到结尾，则返回true，如果t先到结尾则返回false。

代码如下：

public class Solution {
    public boolean isSubsequence(String s, String t) {
        if (s == null || s.length() == 0) {
            return true;
        }

        if (t == null || t.length() == 0) {
            return false;
        }

        int index = 0;
        for (int i = 0; i < s.length(); i++) {
            char curt = s.charAt(i);
            while (index < t.length() && t.charAt(index) != curt) {
                index++;
            }
            if (index == t.length()) {
                return false;
            }
            index++;
        }

        return true;
    }
}