392. Is Subsequence

Problem

Tags: Two Pointers, String, Dynamic Programming

Given two strings s and t, return true if s is a subsequence of t, or false otherwise.

A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., "ace" is a subsequence of "abcde" while "aec" is not).

Example 1:

Input: s = "abc", t = "ahbgdc"
Output: true

Example 2:

Input: s = "axc", t = "ahbgdc"
Output: false

Constraints:

• 0 <= s.length <= 100
• 0 <= t.length <= 10^4
• s and t consist only of lowercase English letters.

Follow up: Suppose there are lots of incoming s, say s1, s2, ..., sk where k >= 10^9, and you want to check one by one to see if t has its subsequence. In this scenario, how would you change your code?

Code

C

// 392. Is Subsequence (12/19/54135)
// Runtime: 4 ms (29.21%) Memory: 5.76 MB (0.00%) 

bool isSubsequence (char* s, char* t) {
    int s_len = strlen(s), t_len = strlen(t), matched = 0;
    
    if (s_len == 0) {
        return true;
    }
    
    for (int i = 0; i < t_len; i++) {
        if (t[i] == *(s + matched)) {
            matched++;
        }
        
        if (matched >= s_len) {
            return true;
        }
    }
    
    return false;
}