392

392. Is Subsequence (Easy)

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 <= 104
• 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?

Companies:
Adobe, Amazon, Google

Related Topics:
Two Pointers, String, Dynamic Programming

Similar Questions:

• Number of Matching Subsequences (Medium)
• Shortest Way to Form String (Medium)

Solution 1. Two Pointers

// OJ: https://leetcode.com/problems/is-subsequence/
// Author: github.com/lzl124631x
// Time: O(M + N)
// Space: O(1)
class Solution {
public:
    bool isSubsequence(string s, string t) {
        int i = 0, j = 0, M = s.size(), N = t.size();
        for (; i < M && j < N; ++j) {
            if (s[i] == t[j]) ++i;
        }
        return i == M;
    }
};