2021 NAVER漫画開発チャレンジ1回コードテスト3回

import java.util.*;


public class Solution {
    public int solution(String s, String t) {
        int count = 0;

        StringBuilder builder = new StringBuilder();

        int index = 0;
        int block_length = t.length();
        while(index < s.length()) {
            builder.append(s.charAt(index++));
            // continue if current string's length not enough to check target.
            if(builder.length() < block_length) {
                continue;
            }

            // if built string is long enough to check block.
            // check changing block found.
            int startIndex = builder.length() - block_length;
            int endIndex = builder.length();// - 1; substring is exclusive

            // if target string is found, remove from builder and count.
            if(builder.substring(startIndex, endIndex).equals(t)) {
                count++;
                builder.delete(startIndex, endIndex);
            }      

        }

        return count;
    }
}