IsSubsequence.cpp

//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 s is 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?

#include<vector>
#include<algorithm>

using namespace std;

class IsSubsequence {
public:
	bool isSubsequence(string s, string t) {
		int m = s.size(), n = t.size();
		int i = 0, j = 0;
		while (i < m && j < n){
			if (s[i] == t[j]){
				++i;
			}
			++j;
		}
		if (i == m) return true;
		return false;
	}
};