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 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.

1. Analyse

A for loop ?!

2. AC Code

(12 Lines)

class Solution {
public:
    bool isSubsequence(string s, string t) {
		int index = 0;
 		for( int i=0; i<s.size(); i++ ){
			index = t.find( s[i], index )+1;
			if( 0 == index )
				return false;
		}       
		return true;
    }
};

The only trick here is string::find will find the string from index argument2. We need to add 1 when using the index next time.