【题解】HDU-1686 Oulipo

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HDU-1686 Oulipo 类型 KMP

Oulipo (HDU - 1686)

题面

The French author Georges Perec (1936–1982) once wrote a book, La disparition, without the letter 'e'. He was a member of the Oulipo group. A quote from the book:

Tout avait Pair normal, mais tout s’affirmait faux. Tout avait Fair normal, d’abord, puis surgissait l’inhumain, l’affolant. Il aurait voulu savoir où s’articulait l’association qui l’unissait au roman : stir son tapis, assaillant à tout instant son imagination, l’intuition d’un tabou, la vision d’un mal obscur, d’un quoi vacant, d’un non-dit : la vision, l’avision d’un oubli commandant tout, où s’abolissait la raison : tout avait l’air normal mais…

Perec would probably have scored high (or rather, low) in the following contest. People are asked to write a perhaps even meaningful text on some subject with as few occurrences of a given “word” as possible. Our task is to provide the jury with a program that counts these occurrences, in order to obtain a ranking of the competitors. These competitors often write very long texts with nonsense meaning; a sequence of 500,000 consecutive 'T's is not unusual. And they never use spaces.

So we want to quickly find out how often a word, i.e., a given string, occurs in a text. More formally: given the alphabet {'A', 'B', 'C', …, 'Z'} and two finite strings over that alphabet, a word W and a text T, count the number of occurrences of W in T. All the consecutive characters of W must exactly match consecutive characters of T. Occurrences may overlap.

输入

The first line of the input file contains a single number: the number of test cases to follow. Each test case has the following format:

One line with the word W, a string over {'A', 'B', 'C', …, 'Z'}, with 1 ≤ |W| ≤ 10,000 (here |W| denotes the length of the string W). One line with the text T, a string over {'A', 'B', 'C', …, 'Z'}, with |W| ≤ |T| ≤ 1,000,000.

输出

For every test case in the input file, the output should contain a single number, on a single line: the number of occurrences of the word W in the text T.

样例输入

1
2
3
4
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7
3
BAPC
BAPC
AZA
AZAZAZA
VERDI
AVERDXIVYERDIAN

样例输出

1
2
3
1
3
0

提示

无

思路

KMP模板题

代码

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char s[mxn], t[mxn];
int nxt[mxn];

void getnxt(char* t, int m)
{
    int i = 0, j = -1; nxt[0] = -1;
    while (i < m)
    {
        if (j == -1 || t[i] == t[j]) {
            i++, j++;
            // if (t[i] == t[j])
            //     nxt[i] = nxt[j]; // next数组优化
            // else
                nxt[i] = j;
        } else
            j = nxt[j];
    }
}

int KMP(char* s, char* t, int n, int m)
{
    int i = 0, j = 0, ans = 0;
    while (i < n)
    {
        if (j == -1 || s[i] == t[j]) {
            i++, j++;
            if (j >= m) {   // 匹配
                ans++;
                j = nxt[j];
                // return i-j;
            }
        } else
            j = nxt[j];
    }
    return ans;
    // return -1;
}

int main()
{
    int T; scanf("%d", &T);
    while(T--)
    {
        scanf("%s%s", t, s);
        int tl = strlen(t), sl = strlen(s);
        getnxt(t, tl);
        printf("%d\n", KMP(s, t, sl, tl));
    }
    return 0;
}