LeetCode賽題392---- Is Subsequence

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

該問題的算法還是很簡單的，直接從s和t的首端開始遍歷比較字符是否相等即可，如果不等，則增加在t中的下標位置；如果相等，則同時增加在s和t中的下標位置。如果t中的指標位置增長到了t的末尾，而s中的指標還沒有增長的末尾，則返回false。如果s中的指標先增長到了末尾，則返回true。

Java算法實現

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;
    }
}