题目
Is Subsequence
难度 Medium
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?
实现思路
对于字符串s，设置一个index记录其当前已匹配的下标，初始化为0.遍历字符串t，由于子串的顺序与在t中的顺序一样，因此顺序遍历字符串t，若匹配一个字符串s中的字符，index就加一。最后判断index是否等于字符串s的长度。如果是，说明字符串s中的每个字符都可以在s中匹配上，则返回true；否则返回false。
实现代码
bool isSubsequence(string s, string t) {
int index = 0;
if (s.length()>t.length())
return false;
for (int i = 0; i < t.length(); i++) {
if (t[i] == s[index]) {
index++;
}
if (index==s.length()) break;
}
return index==s.length();
}