392. Is Subsequence

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 >= 109, and you want to check one by one to see if t has its subsequence. In this scenario, how would you change your code?

Solution

• two pointer 사용 ==> sp, tp

Code

C++

class Solution
{
public:
    bool isSubsequence(string s, string t)
    {
        int sp = 0;
        int tp = 0;

        while (sp < s.length() && tp < t.length())
        {
            if (s[sp] == t[tp])
            {
                sp++;
            }
            tp++;
        }
        return sp == s.length();
    }
};