【HDU1711】Number Sequence

题面

https://vjudge.net/problem/HDU-1711

题解

#include<cstdio>
#include<iostream>
#include<cstring>
#define ri register int
#define N 1000500
using namespace std;
int T,nex[N],n,m;
int s[N],t[N];

void getnex(){
  nex[0]=nex[1]=0;
  for (ri i=2;i<=n;i++) {
    int j=nex[i-1];
    while (j && s[j+1]!=s[i]) j=nex[j];
    if (s[j+1]==s[i]) nex[i]=j+1; else nex[i]=0;
  }
}

int main(){
  scanf("%d",&T);
  while (T--) {
    scanf("%d",&m);scanf("%d",&n);
    for (ri i=1;i<=m;i++) scanf("%d",&t[i]);
    for (ri i=1;i<=n;i++) scanf("%d",&s[i]);
    getnex();
    int k=0;
    bool ss=0;
    for (ri i=1;i<=m;i++) {
      while (k && s[k+1]!=t[i]) k=nex[k];
      if (s[k+1]==t[i]) {
        k++;
        if (k==n) {
          k=nex[k];
          printf("%d\n",i-n+1);
          ss=1;
          break;
        }
      }
    }
    if (!ss) puts("-1");
  }
  return 0;
}