【两次过】Lintcode 1263. Is Subsequence

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).

样例

Example 1:
s = "abc", t = "ahbgdc"

Return true.

Example 2:
s = "axc", t = "ahbgdc"

Return false.

挑战

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?

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解题思路：

遍历一遍t，如果两指针指向的值相等，则同时加加，继续考察下一组元素，否则只加pt，最后若ps指向末尾了，说明true，否则为false。

class Solution {
public:
    /**
     * @param s: the given string s
     * @param t: the given string t
     * @return: check if s is subsequence of t
     */
    bool isSubsequence(string &s, string &t) 
    {
        // Write your code here
        if(s.empty())
            return true;
        
        for(int pt = 0,ps = 0;pt < t.size();pt++)
        {
            if(s[ps] == t[pt])
                ps++;
                
            if(ps == s.size())
                return true;
        }
        
        return false;
    }
};