poj 3080 Blue Jeans

题目就是找n个字符串的最长公共字串，如果有多个就输出字典序最小的一个。

我的思路就是枚举所有的字串，然后用KMP挨个字符串匹配。

#include <stdio.h>
#include <string.h>

char str[20][70];
char tmp[70];
char ans[70];
int f[70];
int n;

void getfail(char *s)
{
    int m = strlen(s);
    f[0] = 0; f[1] = 0;
    for (int i = 1; i < m; i++)
    {
        int j = f[i];
        while (j && s[j] != s[i]) j = f[j];
        f[i+1] = s[i] == s[j] ? j+1 : 0;
    }
}

bool kmp(char *s)
{
    int m = strlen(tmp);
    int len = strlen(s);
    int j = 0;
    for (int i = 0; i < len; i++)
    {
        while (j && s[i] != tmp[j]) j = f[j];
        if (s[i] == tmp[j])
            j++;
        if (j == m)
            return true;
    }
    return false;
}

bool check()
{
    for (int i = 2; i <= n; i++)
    {
        if (!kmp(str[i]))
            return false;
    }
    return true;
}

int main()
{
    int t;
    scanf("%d", &t);
    while (t--)
    {
        scanf("%d", &n);
        for (int i = 1; i <= n; i++)
        {
             scanf("%s", str[i]);
        }
        int len = strlen(str[1]);
        bool getans = false;
        int anslen = 0;
        for (int i = len; i >= 1; i--)
        {
            for (int j = 0; j <= len-i; j++)
            {
                memset(tmp, '', sizeof(tmp));
                strncpy(tmp, str[1]+j, i);
                if (i < anslen)
                    break;
                if (check())
                {
                    if (!getans)
                    {
                        strcpy(ans, tmp);
                        getans = true;
                        anslen = strlen(ans);
                    }
                    else
                    {
                        if (strcmp(ans, tmp) > 0)
                            strcpy(ans, tmp);
                    }
                }
            }
        }
        if (strlen(ans) >= 3 && getans)
            puts(ans);
        else
            puts("no significant commonalities");
    }
}