LeetCode 392. Is Subsequence

392. Is Subsequence

一、问题描述

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).

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?

二、输入输出

Example 1:
s = "abc", t = "ahbgdc"

Return true.

Example 2:
s = "axc", t = "ahbgdc"

Return false.

三、解题思路

• 在t中挨个找s里出现的字符。c++ find_first_of可以用来完成这件事情。而且还可以指定查找的起始位置，非常好用，尤其适用于这道题。
• 如果某个字符没有找到，就返回false 如果全部都找完了还没有返回，就返回true

class Solution {public:    bool isSubsequence(string s, string t) {        size_t found = -1;        for (int i = 0, n = s.size(); i < n; ++i) {            char ch = s.at(i);            found = t.find_first_of(ch, found+1);            if(found == string::npos)return false;        }        return true;    }};