392. Is Subsequence

O(t.length)

class Solution {
public:
    bool isSubsequence(string s, string t) {
        int m = s.length(), n = t.length(), i = 0, j = 0;
        if (m > n) return false;
        for (; i < m && j < n; ++j) {
            if (s[i] == t[j]) {
                ++i;
            }
        }
        return i == m;
    }
};

class Solution {
public:
    bool isSubsequence(string s, string t) {
        int i_t = 0;
        for (auto&& c : s) {
            while (i_t < t.length() && t[i_t] != c) ++i_t;
            if (i_t++ >= t.length()) return false;
        }
        return true;
    }
};