dev/leetcode/substring

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 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?

Overtime

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
class Solution {
public boolean isSubsequence(String s, String t) {
if (s.length() == 0) return true;

for (int i = 0; i < t.length() - s.length(); i++) {
int res = 0;
int cur = i;
while (cur < t.length() && res < s.length()) {
if (t.charAt(cur) == s.charAt(res)) res++;

cur++;

if (res == s.length()) return true;
}
}

return false;
}
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
class Solution {
public boolean isSubsequence(String s, String t) {
int res = -1;
for (int i = 0; i < s.length(); i++) {
res = t.indexOf(s.charAt(i), res + 1);
if (res == -1) return false;
}
return true;
}
}
/*
执行用时 :1 ms, 在所有 Java 提交中击败了90.09%的用户
内存消耗 :44.2 MB, 在所有 Java 提交中击败了100.00%的用户
*/

Reference
https://leetcode-cn.com/problems/is-subsequence