main.cpp

// Source: https://leetcode.com/problems/is-subsequence
// Title: Is Subsequence
// Difficulty: Easy
// Author: Mu Yang <http://muyang.pro>

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// 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?
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

#include <string>

using namespace std;

class Solution {
 public:
  bool isSubsequence(string s, string t) {
    int n = s.size(), m = t.size();

    auto i = 0, j = 0;
    while (i < n && j < m) {
      if (s[i] == t[j]) ++i;
      ++j;
    }
    return i == n;
  }
};