題：https://leetcode.com/problems/is-subsequence/description/

題目

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?

題目大意

字串 s 是否是 t 的子序列。

思路

貪心演算法
按順序從s中取出一個元素c，從左往右找 t 中出現的 相同元素，若未找到返回false。繼續從s中抽取下一個元素，從左往右找 t 中出現的 相同元素且本次起點為上次 t中所找元素的後一位。

class Solution {
    public boolean isSubsequence(String s, String t) {
        for(int i = 0,j =0 ; i < s.length();i++){
            while(j<t.length()){
                if
 
(t.charAt(j) == s.charAt(i))
                    break;
                j++;
            }
            if(j == t.length())
                return false;
            j++;
        }
        return true;     
    }
}