暴力

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
bool  m_strstr(char* des, char* src, int n)
{
    int tmp = 0;
    char* p = src;
    while (*des)
    {
        if (*des == *p)
        {
            des++;
            p++;
            tmp++;
            if (tmp == n)  return true;
            continue;
        }
        des++;
        p = src;
    }
    return false;
}
int main()
{
    char str1[100] = { 0 };
    char str2[100] = { 0 };
    scanf("%s%s", str1, str2);
    int len1 = strlen(str1);
    int len2 = strlen(str2);

    char* p = str1, * q = str2;//p指向短的一个字符串
    if (len1 > len2)
    {
        p = str2, q = str1;
        swap(len1, len2);
    }
    int cnt = 0;//字串的大小
    char* res = NULL;//字串的起始位置
    for (int i = 1;i <= len1; i++)
    {
        for (int j = 0; j < len1-i; j++)
        {
            if (m_strstr(q, p + j, i))//匹配成功
            {
                cnt = max(cnt, i);//更新
                if (cnt == i)
                {
                    res = p + j;
                }

            }
        }

    }
    if (res != NULL)
    {
        for (int i = 0; i < cnt; i++)  putchar(*res++);
    }

    return 0;
}