 # Subsequence - 392. Is Subsequence

1. 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 tt 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`.

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?

Credits:
Special thanks to @pbrother for adding this problem and creating all test cases.

java：

``````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 < t.length(); i++) {
if (s.charAt(index) == t.charAt(i)) index++;
if (index == s.length()) return true;
}

return false;*/

int prev = -1;
for (int i = 0; i < s.length(); i++) {
int index = t.indexOf(s.charAt(i), prev+1);
if (index < 0) {
return false;
}
prev = index;
}
return true;
}
}
``````

Nothing just happens, it's all part of a plan.