POJ 3450 Corporate Identity

二分枚举+KMP

之前没注意字典序最小，WA了N次……

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>

using namespace std;

const int MAXN = 4010;
const int MAXL = 210;

int N;
char str[MAXN][MAXL];
char temp[MAXL];
char anser[MAXL];
int nextval[MAXL];
int len[MAXN];

void GetNextVal( char *s, int lenth )
{
    int i = 0, j = -1;
    nextval[0] = -1;
    while ( i < lenth )
    {
        if ( j == -1 || s[i] == s[j] )
        {
            ++i, ++j;
            if ( s[i] != s[j] ) nextval[i] = j;
            else nextval[i] = nextval[j];
        }
        else j = nextval[j];
    }
    return;
}

bool KMP( char *t, char *s, int lenth, int lenn )
{
    GetNextVal( t, lenth );
    int i = 0, j = 0;
    while ( j < lenn )
    {
        if ( i == -1 || s[j] == t[i] )
        {
            ++i, ++j;
            if ( i == lenth ) return true;
        }
        else i = nextval[i];
        //if ( i == lenth ) return true;
    }
    return false;
}

bool check( int tpL )
{
    bool flag = false;
    bool ok = false;
    for ( int st = 0; st + tpL - 1 < len[0]; ++st )
    {
        for ( int k = 0; k < tpL; ++k )
            temp[k] = str[0][ st + k ];
        temp[ tpL ] = '\0';
        //puts(temp);

        ok = true;
        for ( int i = 1; i < N; ++i )
            if ( !KMP( temp, str[i], tpL, len[i] ) )
            {
                ok = false;
                break;
            }
        if ( ok )
        {
            flag = true;
            if ( anser[0] == '\0' ||
                ( strlen(anser) == strlen(temp) && strcmp( anser, temp ) > 0 ) || ( strlen(anser) < strlen(temp) ) )
                strcpy( anser, temp );
        }
    }
    return flag;
}

int main()
{
    while ( scanf( "%d", &N ), N )
    {
        int bound = 1 << 30;
        for ( int i = 0; i < N; ++i )
        {
            scanf( "%s", str[i] );
            len[i] = strlen( str[i] );
            bound = min( bound, len[i] );
        }

        int low = 0;
        int high = bound;
        int mid, ans = 0;
        anser[0] = '\0';
        while ( low <= high )
        {
            mid = ( low + high ) >> 1;
            if ( check( mid ) )
            {
                ans = mid;
                low = mid + 1;
            }
            else high = mid - 1;
        }

        if ( !ans ) puts("IDENTITY LOST");
        else puts(anser);
    }
    return 0;
}