Is-Subsequence

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LeetCode#392 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 sis 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?

解题思路

  这道题是一道Medium，但是却非常的简单，定义指向S和T的指针，当他们所对应的字符相等时，两个指针都自增1，当他们不相等的时候T的指针自增。最后判断S的指针是否走到了最后就可以了。

解题代码【.CPP】

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//runtime:72ms
class Solution {
public:
    bool isSubsequence(string s, string t) {
        int idxs = 0 , idxt = 0;
        while (idxs < s.size() && idxt < t.size()){
            if(s[idxs] == t[idxt]){
                ++idxs;
                ++idxt;
            } else {
                ++idxt;
            }
        }
        return idxs == s.size();
    }
};
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