392. Is Subsequence

Problem:

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?

思路：

Solution (C++):

bool isSubsequence(string s, string t) {
    int m = s.length(), n = t.length(), i = 0, j, temp = 0;
    for (i; i < m; ++i) {
        for (j = temp; j < n; ++j) {
            if (t[j] == s[i]) { temp = j + 1; break; }
        }
        if (j == n) return false;
    }
    return true;
}

性能：

Runtime: 60 ms  Memory Usage: 15.1 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB