Leetcode392. Is Subsequence

Description

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.

My program:

从s和t的首端开始遍历比较字符是否相等即可，如果不等，则增加在t中的下标j位置；如果相等，则同时增加s中下标i和t中下标j。如果t中的指标位置增长到了t的末尾，而s中的指标还没有增长的末尾，则返回false。如果s中的指标先增长到了末尾，则返回true。

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

Simple C++ code:

bool isSubsequence(string s, string t) {
        int si= 0;
        for(int ti = 0; ti < t.size() && si < s.size(); ti++) {
            if(t[ti] == s[si]) si++;
        }
        return si == s.size();
    }