LCS 算法应用，求出最长公共子串，而非长度。

LCS 算法轨迹，来自算法导论

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * 题意：把两个单词拼接成一个新单词，使得新单词的子序列中包含两个单词，并且要使这个新单词最短
 *
 * 思路：先利用 LCS 算法求出最长公共子串，然后拼接输出即可。
 *
 */
public class Main {

    private static int[][] maxLen = new int[1000][1000];

    private static String work(String str1, String str2) {
        StringBuilder result = new StringBuilder();
        char[] ch1 = str1.toCharArray();
        char[] ch2 = str2.toCharArray();
        int length1 = ch1.length;
        int length2 = ch2.length;
        // 正常 LCS 算法
        for (int indexI = 1; indexI <= length1; indexI++) {
            for (int indexJ = 1; indexJ <= length2; indexJ++) {
                if (ch1[indexI - 1] == ch2[indexJ - 1]) {
                    maxLen[indexI][indexJ] = maxLen[indexI - 1][indexJ - 1] + 1;
                } else {
                    maxLen[indexI][indexJ] = Math.max(maxLen[indexI - 1][indexJ], maxLen[indexI][indexJ - 1]);
                }
            }
        }
        // 规则处理：当没有最长公共子串时，输出两个字符串全部字符。
        if (maxLen[length1][length2] == 0) {
            result.append(str1).append(str2);
        } else {
            int indexI = length1;
            int indexJ = length2;
            // 反向进行比较
            while (indexI > 0 && indexJ > 0) {
                // 将最长公共子串字符拼接到 result
                if (maxLen[indexI][indexJ] == maxLen[indexI - 1][indexJ - 1] + 1 && ch1[indexI - 1] == ch2[indexJ - 1]) {
                    result.append(ch1[indexI - 1]);
                    indexI--;
                    indexJ--;
                } else {
                    // 将两个字符串中字符（不属于最长公共子串的字符）拼接到 result
                    if (maxLen[indexI][indexJ] == maxLen[indexI - 1][indexJ]) {
                        result.append(ch1[--indexI]);
                    } else {
                        result.append(ch2[--indexJ]);
                    }
                }
            }
            // 将剩余的字符全部存储到 result
            while (indexI > 0) {
                result.append(ch1[--indexI]);
            }
            while (indexJ > 0) {
                result.append(ch2[--indexJ]);
            }
        }
        return result.reverse().toString();
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
        PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
        String str1;
        String str2;
        while (in.hasNext()) {
            str1 = in.next();
            str2 = in.next();
            out.println(work(str1, str2));
        }
        out.flush();
    }
}