滑动窗口[start, end),如果符合,就扩充,否则移动窗口start++

import java.util.*;


public class Solution {
    /**
     * longest common substring
     * @param str1 string字符串 the string
     * @param str2 string字符串 the string
     * @return string字符串
     */
    public String LCS (String text1, String text2) {
        // write code here
        int start = 0;
        int end = 1;
        String ans = "";
        while(end <= text2.length()) {
            String sub = text2.substring(start, end);
            if (text1.contains(sub)) {
                ans = sub;
            } else{
                start++;
            }
            end++;
        }
        return ans;
    }
}