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.

 

判断字符串s是否是字符串t的子串，要求顺序不能颠倒。双指针遍历。

class Solution {
public:
    bool isSubsequence(string s, string t) {
        if(t.size()<s.size())   return false;
        if(s.size()==0||t.size()==0) return true;
        
        int indexS = 0;
        int indexT = 0;
        
        while(indexT <= t.size()){
            if(indexS == s.size()){
                return true;
            }
            
            if(s[indexS] == t[indexT]){
                indexS++;
                indexT++;
            }else if(s[indexS] != t[indexT]){
                indexT++;
            }
        }
        
        return false;
    }
};