的标题是太可怕了，我知道，但直到我知道回答我的问题，我想不出一个更好的。如果可以，请编辑。

我在OnlineJudge网站的一个解决（好玩）一个非常简单的问题。问题是这样的：

I was solving (for fun) a very easy problem on one of OnlineJudge sites. The problem is this:

输入：包含一个字符串   小写拉丁字母。的长度   串为至少1且至多100   输出：单号也就是   的最长子串的长度   其发生在至少输入字符串   两次在该字符串（该事件可能会重叠）。

Input: a single string containing lowercase latin letters. The length of string is at least 1 and at most 100. Output: a single number which is the length of the longest substring of the input string which occurs at least twice in that string( the occurrences may overlap).

样品输入：贝巴 示例输出： 3

Sample input: ababa Sample output: 3

我的的接受的有以下code：

I got Accepted with the following code:

#include <iostream>
#include <string>
#include <algorithm>
int main()
{
    std::string s;
    std::cin >> s;
    int max = 0;
    typedef std::string::const_iterator sit;
    sit end = s.end();
    for(sit it1 = s.begin(); it1 != end; ++it1)
        for(sit it2 = it1 + 1; it2 != end; ++it2)
            max = std::max(max, std::mismatch(it1, it1 + (end - it2), it2).first - it1);
    std::cout << max;
}

不过，我得到的的在测试42运行时错误 （我不知道是什么输入的是 - 网站规则）具有以下code这不过是稍有不同的第一个。

However, I get Runtime Error on Test 42 (I can't know what input is that - site rules) with the following code which is but slightly different from the first one.

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
using namespace std;

int main()
{
    string s;
    cin >> s;
    vector<size_t> dif;
    for(string::const_iterator it1 = s.begin(); it1 != s.end(); ++it1)
        for(string::const_iterator it2 = it1 + 1; it2 != s.end(); ++it2)
            dif.push_back(mismatch(it1, it1 + (s.end() - it2), it2).first - it1);
    cout << *max_element(dif.begin(), dif.end());
}

祭祀舞蹈半个多小时后，我放弃了。我想不出有什么不对的第二code（除非是的略少有效的可读性的事实）。难道是我减去一个常量性从迭代？或者是因为INT主场迎战为size_t的？在code编译（在他们的网站）与MSVC8.0或9.0。释放模式。有任何想法吗？谢谢你。

After half an hour of ritual dancing, I give up. I can't figure out what's wrong with the second code (except the fact that is's slightly less effective and less readable). Is it that I am substracting a const_iterator from an iterator? Or because of int vs. size_t? The code is compiled (on their site) with MSVC8.0 or 9.0. Release mode. Any ideas? Thanks.

推荐答案

在不运行您的code，我觉得长度为1的输入字符串你的第二个解决方案失败。

Without running your code, I think your second solution fails on input strings of length 1.

您 DIF 载体是空的，只要输入字符串长度为1，这会导致 * max_element（dif.begin（），dif.end（ ））失败。

Your dif vector is empty whenever the input string has length 1, which causes *max_element(dif.begin(), dif.end()) to fail.