LeetCode 392. Is Subsequence

原题链接在这里：https://leetcode.com/problems/is-subsequence/description/

题目：

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?

题解：

Two pointers. 当所指char相同就移动s的index, 看s的index能不能移动到末尾.

Time Complexity: O(s.length()+t.length()).

Space: O(1).

AC 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 i = 0; 
        int j = 0;
        while(j < t.length()){
            if(s.charAt(i) == t.charAt(j)){
                i++;
                if(i == s.length()){
                    return true;
                }
            }
            j++;
        }
        return false;
    }
}

 类似Shortest Way to Form String.