#HDU 1711 Number Sequence（KMP）

Given two sequences of numbers : a[1], a[2], ...... , a[N], and b[1], b[2], ...... , b[M] (1 <= M <= 10000, 1 <= N <= 1000000). Your task is to find a number K which make a[K] = b[1], a[K + 1] = b[2], ...... , a[K + M - 1] = b[M]. If there are more than one K exist, output the smallest one.

Input

The first line of input is a number T which indicate the number of cases. Each case contains three lines. The first line is two numbers N and M (1 <= M <= 10000, 1 <= N <= 1000000). The second line contains N integers which indicate a[1], a[2], ...... , a[N]. The third line contains M integers which indicate b[1], b[2], ...... , b[M]. All integers are in the range of [-1000000, 1000000].

Output

For each test case, you should output one line which only contain K described above. If no such K exists, output -1 instead.

Sample Input

2 13 5 1 2 1 2 3 1 2 3 1 3 2 1 2 1 2 3 1 3 13 5 1 2 1 2 3 1 2 3 1 3 2 1 2 1 2 3 2 1

Sample Output

6 -1

题目大意：一共由T个测试数据，输入两个数组的长度N， M，再分别输入两个数组（从1 到 N 和 1 到 M），如果数组2是数组1的子集，则输入第一个匹配的下表，如果不是，输出 -1

思路：典型的KMP，这道题要注意的就是是从1 到 N和 1 到 M输入的，而不是字符串里的0开始，所以nxt的初始化也要更改，可以全部设为1，然后所有i 和 j都往后移一位就可以了，直到匹配的长度等于数组 2 的长度，输出这时候 i 所在的位置 - 数组2的长度。KMP基础题

AC代码：

#include<iostream>
#include<cstring>
using namespace std;
const int maxn = 1e4 + 5;
const int maxm = 1e6 + 5;

int a[maxm], b[maxn], nxt[maxn];
int n, m, T;
void getnext() {
    nxt[1] = 0;
    int i = 1, j = 0;
    while (i <= m) {
        if (!j || b[i] == b[j])
            nxt[++i] = ++j;
        else
            j = nxt[j];
    }
}
int KMP() {
    getnext();
    int i = 1, j = 1, sum = 0;
    while (i <= n) {
        if (!j || a[i] == b[j])
            ++i, ++j;
        else
            j = nxt[j];
        if (j == m + 1) return i - m;
    }
    return -1;
}

int main()
{
    scanf("%d", &T);
    while (T--) {
        scanf("%d%d", &n, &m);
        memset(nxt, -1, sizeof(nxt));
        for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
        for (int i = 1; i <= m; i++) scanf("%d", &b[i]);
        cout << KMP() << endl;
    }
    return 0;
}

#HDU 1711 Number Sequence（KMP）

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