Description
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?
Credits:
Special thanks to @pbrother for adding this problem and creating all test cases.
Solution
Two-pointer, time O(m + n), space O(1)
起初用DP做过了，后来发现并不需要，双指针法就可以解决了。
class Solution {
public boolean isSubsequence(String s, String t) {
int i = 0;
for (int j = 0; j < t.length() && i < s.length(); ++j) {
if (s.charAt(i) == t.charAt(j)) {
++i;
}
}
return i == s.length();
}
}
