leetcode學習篇十——Is Subsequence

題目：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.

難度：medium 通過率：43.8%

這道題想法比較簡單，直接對兩個字符串進行對比判斷，通過一個while循環語句就可以寫出來，用count按順序記錄相同的個數，就可以得出結果。實現如下：算法複雜度：O(n)

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