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.
算法分析
该问题的算法还是很简单的，直接从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中的下标位置；如果相等，则同时增加在s和t中的下标位置。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。
Java算法实现
public class Solution {
public boolean isSubsequence(String s, String t) {
if(s==null||s.length()==0)
return true;
int index=0;
char ch;
for(int i=0;i<s.length();i++){
ch=s.charAt(i);
while(index<t.length()&&t.charAt(index)!=ch){
index++;
}
if(index>=t.length()){
return false;
}
index++;
}
return true;
}
}