LeetCode 392. Is Subsequence 题解

392. Is Subsequence

 

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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.

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?

题目分析：

如果s是t的子序列，那么j中会按s中字符的顺序依次包含s的每个字符。由此可得一O(n)算法。注意s为空字符串时的特殊情况。

代码展示：

class Solution {public:    bool isSubsequence(string s, string t) {        int s1 = s.size();        int s2 = t.size();        if(!s1) return true;        int j=0;        int i=0;        while(j<t.size())        {            if(t[j]==s[i])            {                i++;                j++;                if(i==s1) return true;            }            else            {                j++;            }        }        return false;    }};