题解 | #查找两个字符串a,b中的最长公共子串#

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.LinkedHashMap;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(
                    System.in));
        String str;
        while ((str = bufferedReader.readLine()) != null) {
            String str2 = bufferedReader.readLine();
            // 拿到短字串 最先出现的那个最长字串，所以先遍历短字串
            if (str.length() < str2.length()) {
                getLongSon(str, str2);
            } else {
                getLongSon(str2, str);
            }
        }
    }

    private static void getLongSon(String str, String str2) {
        int max = 0;
        LinkedHashMap<Integer, Point> lhm = new LinkedHashMap<>();
        for (int i = 0; i < str.length(); i++) {
            for (int j = 0; j < str2.length(); j++) {
                int l = i;
                int r = j;
                while (l < str.length() && r < str2.length() &&
                        str.charAt(l) == str2.charAt(r)) {
                    l++;
                    r++;
                }
                // 最后一次不满足条件，l需要回滚
                l--;
                if (l - i + 1 > max) {
                    max = l - i + 1;
                    // 传入l+1方便后面截取
                    lhm.put(max, new Point(i, l + 1));
                }
            }
        }
        Point point = lhm.get(max);
        System.out.println(str.substring(point.x, point.y));
    }

    static class Point {
        int x;
        int y;

        public Point(int x, int y) {
            this.x = x;
            this.y = y;
        }
    }
}