1. description

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?

2. solution:

此題比較簡單，記錄一下，不多說。

class Solution {
public:
    bool isSubsequence(string s, string t) {

    if(s.length() == 0) return true;
    if(t.length() > 500000) return false;
    int t_len = t.length();
    int s_len = s.length();

    int i = 0, j = 0;
    while(i < s_len && j < t_len) {
        if
 
(s[i] == t[j]) {
            i++;
            j++;
            if(i == s_len)
                return true;
        } else {
            j++;
        }
    }
    return false;

}
};