java - 查找两个候选字符串列表之间的交集

Question

我编写了以下Java代码，以查找String的前缀和后缀之间的交集> 在 Java 中。

// you can also use imports, for example:
// import java.math.*;
import java.util.*;
class Solution {
    public int max_prefix_suffix(String S) {
        if (S.length() == 0) {
            return 1;
        }
        // prefix candidates
        Vector<String> prefix = new Vector<String>();
        // suffix candidates
        Vector<String> suffix = new Vector<String>();
        // will tell me the difference
        Set<String> set = new HashSet<String>();

        int size = S.length();
        for (int i = 0; i < size; i++) {
            String candidate = getPrefix(S, i);
            // System.out.println( candidate );
            prefix.add(candidate);
        }

        for (int i = size; i >= 0; i--) {
            String candidate = getSuffix(S, i);
            // System.out.println( candidate );
            suffix.add(candidate);
        }

        int p = prefix.size();
        int s = suffix.size();
        for (int i = 0; i < p; i++) {
            set.add(prefix.get(i));
        }
        for (int i = 0; i < s; i++) {
            set.add(suffix.get(i));
        }

        System.out.println("set: " + set.size());
        System.out.println("P: " + p + " S: " + s);
        int max = (p + s) - set.size();
        return max;
    }

    // codility
    // y t i l i d o c
    public String getSuffix(String S, int index) {
        String suffix = "";
        int size = S.length();
        for (int i = size - 1; i >= index; i--) {
            suffix += S.charAt(i);
        }

        return suffix;
    }

    public String getPrefix(String S, int index) {
        String prefix = "";
        for (int i = 0; i <= index; i++) {
            prefix += S.charAt(i);
        }

        return prefix;
    }

    public static void main(String[] args) {
        Solution sol = new Solution();
        String t1 = "";
        String t2 = "abbabba";
        String t3 = "codility";

        System.out.println(sol.max_prefix_suffix(t1));
        System.out.println(sol.max_prefix_suffix(t2));
        System.out.println(sol.max_prefix_suffix(t3));

        System.exit(0);
    }
}

一些测试用例是:

String t1 = "";
String t2 = "abbabba";
String t3 = "codility";

预期值为:

1, 4, 0

我的想法是生成前缀候选者并将它们插入 vector ，然后找到后缀候选者并将它们插入 vector ，最后将两个 vector 插入Set，然后计算差异。但是，我得到了 1、7 和 0。有人可以帮我弄清楚我做错了什么吗？

Answer 1

我将你的方法写如下:

public int max_prefix_suffix(String s) {
    final int len = s.length();
    if (len == 0) {
        return 1; // there's some dispute about this in the comments to your post
    }
    int count = 0;
    for (int i = 1; i <= len; ++i) {
        final String prefix = s.substring(0, i);
        final String suffix = s.substring(len - i, len);
        if (prefix.equals(suffix)) {
            ++count;
        }
    }
    return count;
}

如果您需要将前缀与后缀的反向进行比较，我会这样做:

final String suffix = new StringBuilder(s.substring(len - i, len))
    .reverse().toString();