codeves 1204

题意:2个字符串s,t.问t出现在s的首个位置。

思路：KMP模板，当然这里暴力也可以

#include <iostream>
#include <cstring>
using namespace std;

const int N = 1000002;
int next[N];
char S[N], T[N];
int slen, tlen;

void getNext()
{
    int j, k;
    j = 0; k = -1; next[0] = -1;
    while(j < tlen)
        if(k == -1 || T[j] == T[k])
            next[++j] = ++k;
        else
            k = next[k];

}
int KMP_Index()
{
    int i = 0, j = 0;
    getNext();
    while(i < slen && j < tlen)
    {
        if(j == -1 || S[i] == T[j])
        {
            i++; j++;
        }
        else
            j = next[j];
    }
    if(j == tlen)
        return i - tlen;
    else
        return -1;
}

int main()
{
    cin>>S>>T;
    slen = strlen(S);
    tlen = strlen(T);
    cout<<KMP_Index()+1<<endl;
    return 0;
}