Number Sequence - HDU 1711（KMP模板题）

题意：给你一个a串和一个b串，问b串是否是a串的子串，如果是返回b在a中最早出现的位置，否则输出-1

 

分析：应该是最简单的模板题了吧.....

代码如下：

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

const int MAXM = 1e4+7;
const int MAXN = 1e6+7;

int a[MAXN], b[MAXM], next_b[MAXM];

void GetNext(int b[], int next[], int M)
{
    int i=0, j=-1;
    next[0] = -1;

    while(i < M)
    {
        if(j==-1 || b[i]==b[j])
            next[++i] = ++j;
        else
            j = next[j];
    }
}
int KMP(int a[], int b[], int next[], int N, int M)
{
    int i = 0, j = 0;

    while(i < N)
    {
        while(j==-1 || a[i] == b[j] && j<M)
            i++, j++;

        if(j == M)return i-M+1;

        j = next[j];
    }

    return -1;
}

int main()
{
    int T;

    scanf("%d", &T);

    while(T--)
    {
        int i, N, M;

        scanf("%d%d", &N, &M);

        for(i=0; i<N; i++)
            scanf("%d", &a[i]);
        for(i=0; i<M; i++)
            scanf("%d", &b[i]);

        GetNext(b, next_b, M);

        printf("%d\n", KMP(a, b, next_b, N, M));
    }

    return 0;
}