KMP

參考：  http://www.cnblogs.com/BeyondAnyTime/archive/2012/07/09/2583133.html

        http://blog.csdn.net/v_july_v/article/details/7041827#t3    這個較好

以hdu 1711 爲模板

方法一

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
const int maxn = 1e6+9;
const int maxn1 = 1e4+9;
int a[maxn], b[maxn1];
int n, m;
int next[maxn1];

void Next()
{
    next[0] = -1;
    for(int j = 1; j < m; j++)
    {
        int i = next[j-1];
        while(b[j] != b[i+1] && i >= 0) i = next[i];//如果不相等，就如他們匹配不成功，如 1 1 2 1 1 4, 4和2不等
        if(b[j] == b[i+1]) next[j] = i+1;//如同 1 1 2與1 1 4匹配，所以 要 i = next[i];
        else next[j] = -1;
    }
}

int kmp()
{
    Next();
    int p = 0, s = 0;
    while(p < m && s < n)
    {
        if(b[p] == a[s]) p++, s++;
        else
        {
            if(p == 0) s++;
            else p = next[p-1] + 1;
        }
    }
    if(p < m) return -1;
    return s-m;
}

int main()
{
    int t;
    scanf("%d", &t);
    while(t--)
    {
        memset(next, 0, sizeof(next));
        scanf("%d%d", &n, &m);
        for(int i = 0; i < n; i++) scanf("%d", a+i);
        for(int i = 0; i < m; i++) scanf("%d", b+i);
        int w = kmp();
        printf("%d\n", w==-1?-1:w+1);
    }
    return 0;
}

方法二

#include <iostream>
#include <cstdio>
using namespace std;
const int maxn = 1e6+9;
const int maxn1 = 1e4+9;
int a[maxn], b[maxn1], n, m;
int nextval[maxn1];

void get_nextval()
{
    int i = 0, j = -1;
    nextval[0] = -1;
    while(i < m)
    {
        if(j == -1 || b[i] == b[j])
        {
             if(b[++i] == b[++j]) nextval[i] = nextval[j];
             else nextval[i] = j;
        }
        else j = nextval[j];
    }
}

void kmp()
{
    get_nextval();
    int i = 0, j = 0;
    while(i < n && j < m)
    {
        if(j == -1 || a[i] == b[j]) ++i, ++j;
        else j = nextval[j];
    }
    if(j == m) printf("%d\n", i-j+1);
    else printf("-1\n");
}

int main()
{
    int t;
    cin >> t;
    while(t--)
    {
        scanf("%d%d", &n, &m);
        for(int i = 0; i < n; i++) scanf("%d", &a[i]);
        for(int i = 0; i < m; i++) scanf("%d", &b[i]);
        kmp();
    }
    return 0;
}